High speed peripheral interconnect apparatus, method and system

ABSTRACT

A multiple use core logic chip set is provided in a computer system that may be configured either as a bridge between an accelerated graphics port (“AGP”) bus and host and memory buses, as a bridge between an additional registered peripheral component interconnect (“RegPCI”) bus and the host and memory buses, or as a bridge between a primary PCI bus and an additional RegPCI bus. The function of the multiple use chip set is determined at the time of manufacture of the computer system or in the field whether an AGP bus bridge or an additional registered PCI bus bridge is to be implemented. The multiple use core logic chip set has an arbiter having Request (“REQ”) and Grant (“GNT”) signal lines for each PCI device utilized on the additional registered PCI bus. Selection of the type of bus bridge (AGP or RegPCI) in the multiple use core logic chip set may be made by a hardware signal input, or by software during computer system configuration or power on self test (“POST”). Software configuration may also be determined upon detection of either an AGP or a RegPCI device connected to the common AGP/RegPCI bus.

BACKGROUND OF THE INVENTION

1. Field if the Invention

The present invention relates to computer systems using a bus bridge(s)to interface a central processor(s), memory and computer peripheralstogether, and more particularly, in utilizing a registered peripheralcomponent interconnect bus, logic circuits therefor and signal protocolsthereof.

2. Description of the Related Technology

Use of computers, especially personal computers, in business and at homeis becoming more and more pervasive because the computer has become anintegral tool of most information workers who work in the fields ofaccounting, law, engineering, insurance, services, sales and the like.Rapid technological improvements in the field of computers have openedup many new applications heretofore unavailable or too expensive for theuse of older technology mainframe computers. These personal computersmay be used as stand-alone workstations (high end individual personalcomputers) or linked together in a network by a “network server” whichis also a personal computer which may have a few additional featuresspecific to its purpose in the network. The network server may be usedto store massive amounts of data, and may facilitate interaction of theindividual workstations connected to the network for electronic mail(“e-mail”), document databases, video teleconferencing, whiteboarding,integrated enterprise calendar, virtual engineering design and the like.Multiple network servers may also be interconnected by local areanetworks (“LAN”) and wide area networks (“WAN”).

Increasingly sophisticated microprocessors have revolutionized the roleof the personal computer by enabling complex applications software torun at mainframe computer speeds. The latest microprocessors havebrought the level of technical sophistication to personal computersthat, just a few years ago, was available only in mainframe andmini-computer systems. Some representative examples of these newmicroprocessors are the “PENTIUM” and “PENTIUM PRO” (registeredtrademarks of Intel Corporation). Advanced microprocessors are alsomanufactured by Advanced Micro Devices, Digital Equipment Corporation,Cyrix, IBM and Motorola. These sophisticated microprocessors have, inturn, made possible running more complex application programs thatrequire higher speed data transfer rates between the centralprocessor(s), main system memory and the computer peripherals.

Personal computers today may be easily upgraded with new peripheraldevices for added flexibility and enhanced performance. A major advancein the performance of personal computers (both workstation and networkservers) has been the implementation of sophisticated peripheral devicessuch as video graphics adapters, local area network interfaces, SCSI busadapters, full motion video, redundant error checking and correctingdisk arrays, and the like. These sophisticated peripheral devices arecapable of data transfer rates approaching the native speed of thecomputer system microprocessor central processing unit (“CPU”). Theperipheral devices' data transfer speeds are achieved by connecting theperipheral devices to the microprocessor(s) and associated system randomaccess memory through high speed expansion local buses. Most notably, ahigh speed expansion local bus standard has emerged that ismicroprocessor independent and has been embraced by a significant numberof peripheral hardware manufacturers and software programmers. This highspeed expansion bus standard is called the “Peripheral ComponentInterconnect” or “PCI.” A more complete definition of the PCI local busmay be found in the PCI Local Bus Specification, revision 2.1; PCI/PCIBridge Specification, revision 1.0; the disclosures of which are herebyincorporated by reference. These PCI specifications are available fromthe PCI Special Interest Group, 2575 NE Kathryn St #17, Hillsboro, Oreg.97124.

The PCI version 2.1 Specification allows for a 33 MHz or 66 MHz, 32 bitPCI bus; and a 33 Mhz or 66 MHz, 64 bit PCI bus. The 33 MHz, 32 bit PCIis capable of up to 133 megabytes per second (“MB/s”) peak and 50 MB/stypical, and the 66 MHz, 32 bit PCI bus; and the 33 MHz, 64 bit PCI busare capable of up to 266 MB/s peak. The PCI version 2.1 Specification,however, only allows two PCI device cards (two PCI connectors) on a 66MHz PCI bus because of timing constraints such as clock skew,propagation delay, input setup time and valid output delay. Typically,the 66 MHz PCI version 2.1 Specification requires the sourcing agent touse a late-arriving signal with a setup time of only 3 nanoseconds(“ns”) to determine whether to keep the same data on the bus or advanceto the next data, with a 6 ns maximum output delay. Current state of theart Application Specific Integrated Circuits (“ASIC”) using 0.5 microntechnology have difficulty meeting the aforementioned timingrequirements. Even using the newer and more expensive 0.35 micron ASICtechnology may be marginal in achieving the timing requirements for the66 MHz PCI bus.

Since the introduction of the 66 MHz timing parameters of the PCISpecification in 1994, bandwidth requirements of peripheral devices havesteadily grown. Devices are beginning to appear on the market thatsupport either a 64-bit bus, 66 MHz clock frequency or both, with peakbandwidth capabilities up to 533 Mbytes/s. Because faster I/Otechnologies such as Gigabit Ethernet and Fiberchannel are on thehorizon, faster system-interconnect buses will be required in thefuture.

When an industry outgrows a widely accepted standard, that industry mustdecide whether to replace the standard or to enhance it. Since therelease of the first PCI Specification in 1992, the PCI bus has becomeubiquitous in the consumer, workstation, and server markets. Its successhas been so great that other markets such as industrial controls,telecommunications, and high-reliability systems have leveraged thespecification and the wide availability of devices into specialtyapplications. Clearly, the preferred approach to moving beyond today'sPCI Local Bus Specification is to enhance it.

What is needed is an apparatus, method, and system for a personalcomputer that provides increased data throughput between the personalcomputer system central processing unit(s), memory and peripherals thatcan operate at speeds significantly higher than today's PCISpecification allows. In addition, the present invention shall still becompatible with and be able to operate at conventional PCI speeds andmodes when installed in conventional computer systems or wheninterfacing with a conventional PCI device(s) or card(s).

SUMMARY OF THE INVENTION

The present invention overcomes the above-identified problems as well asother shortcomings and deficiencies of existing technologies byproviding in a computer system a registered peripheral componentinterconnect bus, logic circuits therefor and signal protocols thereof.In the present invention, hereinafter referenced as Registered PCI(“RegPCI”), all signals are sampled on the rising edge of the PCI busclock and only the registered version of these signals are used insidethe RegPCI devices. In the current PCI 2.1 Specification, there are manycases where the state of an input signal setting up to a particularclock edge affects the state of an output signal after that same clockedge. This type of input-output signal behavior is not possible in aregistered interface, thus RegPCI introduces the concept of a clock-pairboundary which replaces some single-clock-edges where control signalschange. Timing on the RegPCI bus is not as critical as theaforementioned 66 MHz PCI 2.1 Specification, even when the RegPCI busruns faster than 133 MHz. The RegPCI allows PCI bus operation with morethan two PCI device cards.

RegPCI allows for higher clock frequencies such as, for example, 133 MHzin a fully backward-compatible way. RegPCI devices may be designed tomeet Registered PCI requirements and still operate as conventional 33MHz and 66 MHz PCI devices when installed in legacy computer systems.Similarly, if conventional PCI devices are installed in a RegPCI bus,the clock remains at a frequency acceptable to the conventional device,and other devices are restricted to using conventional protocol whencommunicating with the conventional device. It is expected that thishigh degree of backward compatibility will enable the gradual migrationof systems and devices to bandwidths in excess of 1 Gbyte/s.

In the present invention, numerous combinations in control fields arereserved for new features. One such feature, Double Data Rate, hasimportant application to embedded controller designs and smallslot-based systems. For that reason, control fields and signal protocolshave been reserved for its implementation.

An embodiment of the invention contemplates a multiple use core logicchip set which may be one or more integrated circuit devices such as anApplication Specific Integrated Circuit (“ASIC”), Programmable LogicArray (“PLA”) and the like. RegPCI device(s) may be embedded on thecomputer system motherboard, or may be on a separate card(s) which plugsinto a corresponding card edge connector(s) attached to the systemmotherboard and connected to the core logic chip set through the RegPCIbus.

According to the PCI specification, including Registered PCI, all PCIdevices shall implement a base set of configuration registers. The PCIdevice may also implement other required lo or optional configurationregisters defined in the PCI specification. The PCI specification alsodefines configuration registers and information to be contained thereinfor a PCI compliant device so as to indicate its capabilities and systemrequirements. Once the information for all of the bus devices aredetermined, the core logic may be configured as an additional RegPCI businterface by the startup software. This software also determines whetherthe PCI devices operate at [[[[33 MHz or 66 MHz, have a 64 bit or 32 bitaddress and data bus, and if the PCI devices are RegPCI compliant.

Other and further features and advantages will be apparent from thefollowing description of presently preferred embodiments of theinvention, given for the purpose of disclosure and taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a computer system;

FIG. 2 is a schematic diagram in plan view of a printed circuitmotherboard of the computer system of FIG. 1;

FIG. 3 is a schematic timing diagram of a conventional PCI writetransaction;

FIG. 4 is a schematic timing diagram of a Registered PCI writetransaction according to the present invention;

FIG. 5 is a schematic timing diagram of a Byte-Count Write Operationwith No Target Initial Wait States;

FIG. 6 is a schematic timing diagram of a Byte-Count Write Operationwith Target Initial Wait States;

FIG. 7 is a schematic timing diagram of a Byte-Count Memory-ReadTransaction with No Target Initial Wait States;

FIG. 8 is a schematic timing diagram of a Byte-Count Memory-ReadTransaction with Target Initial Wait States;

FIG. 9 is a schematic timing diagram of a Byte-Enable Write Transactionwith No Wait States;

FIG. 10 is a schematic timing diagram of a Byte-Enable Read with TwoTarget Initial Wait States;

FIG. 11 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “A” with 0 Initial Wait States;

FIG. 12 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “B” with 0 Initial Wait States;

FIG. 13 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “C” with 0 Initial Wait States;

FIG. 14 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “Subtractive” with 0 Initial WaitStates;

FIG. 15 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Read Showing Target Decode “A” with 0 Initial Wait States;

FIG. 16 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Read Showing Target Decode “B” with 0 Initial Wait States;

FIG. 17 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Read Showing Target Decode “C” with 0 Initial Wait States;

FIG. 18 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Read Showing Target Decode “Subtractive” with 0 Initial WaitStates;

FIG. 19 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “A” with 2 Initial Wait States;

FIG. 20 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “A” with 4 Initial Wait States;

FIG. 21 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “C” with 2 Initial Wait States;

FIG. 22 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Read Showing Target Decode “A” with 2 Initial Wait States;

FIG. 23 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Read Showing Target Decode “A” with 4 Initial Wait States;

FIG. 24 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Read Showing Target Decode “C” with 2 Initial Wait States;

FIG. 25 is a schematic timing diagram of a Registered PCIConfiguration-Write Transaction;

FIG. 26 is a schematic timing diagram of a Registered PCIConfiguration-Read Transaction;

FIG. 27 is a schematic timing diagram of Calculation of Maximum RetryTime for Split Transactions;

FIG. 28 is a schematic timing diagram of a Byte-Count Transaction with 4or more Data Phases, Initiator Disconnection at ADB or Termination atByte Count;

FIG. 29 is a schematic timing diagram of a Byte-Count TransactionStarting 3 Data Phases from ADB, Initiator Disconnection at ADB orTermination at Byte Count;

FIG. 30 is a schematic timing diagram of a Byte-Count TransactionStarting 2 Data Phases from ADB, Initiator Disconnection at ADB orTermination at Byte Count;

FIG. 31 is a schematic timing diagram of a Byte-Count TransactionStarting 1 Data Phase from ADB, Initiator Disconnection at ADB orTermination at Byte Count;

FIG. 32 is a schematic timing diagram of a Byte-Count Transaction with 4or More Data Phases, Target Disconnect with Data at ADB;

FIG. 33 is a schematic timing diagram of a Byte-Count TransactionStarting 3 Data Phases from ADB, Target Disconnect with Data at ADB,Decode “A,” 0 Initial Wait States;

FIG. 34 is a schematic timing diagram of a Byte-Count TransactionStarting 2 Data Phases from ADB, Target Disconnect with Data at ADB,Decode “A,” 0 Initial Wait States;

FIG. 35 is a schematic timing diagram of a Byte-Count TransactionStarting 1 Data Phases from ADB, Target Disconnect with Data at ADB,Decode “A,” 0 Initial Wait States;

FIG. 36 is a schematic timing diagram of a Byte-Count TransactionShowing Target Retry;

FIG. 37 is a schematic timing diagram of a Byte-Enable TransactionShowing Target Retry;

FIG. 38 is a schematic timing diagram of a Split Response Termination ofa Byte-Count Memory-Read Transaction;

FIG. 39 is a schematic timing diagram of a Master-Abort Termination of aByte-Count Transaction;

FIG. 40 is a schematic timing diagram of a Master-Abort Termination of aByte-Enable Transaction;

FIG. 41 is a schematic timing diagram of a Target-Abort Termination of aByte-Count Transaction;

FIG. 42 is a schematic timing diagram of a Target-Abort Termination of aByte-Enable Transaction;

FIG. 43 is a schematic timing diagram of a 64-bit Read Request with32-bit Transfer Starting on Even DWORD;

FIG. 44 is a schematic timing diagram of a 64-bit Read Request with32-bit Transfer Starting on Odd DWORD;

FIG. 45 is a schematic timing diagram of a 64-bit Write Request with32-bit Transfer Starting on Even DWORD;

FIG. 46 is a schematic timing diagram of a 64-bit Write Request with32-bit Transfer Starting on Odd DWORD;

FIG. 47 is a schematic timing diagram of a Dual Address Cycle 64-bitMemory-Read Transaction;

FIG. 48 is a schematic timing diagram of a Comprehensive ArbitrationExample;

FIG. 49 is a schematic timing diagram of a Bus Parking;

FIG. 50 is a schematic timing diagram of a;

FIG. 51 is a schematic timing diagram of a;

FIG. 52 is a schematic timing diagram of a;

FIG. 53 is a schematic timing diagram of a;

FIG. 54 is a schematic timing diagram of a;

FIG. 55 is a schematic timing diagram of a;

FIG. 56 is a schematic timing diagram of a;

FIG. 57 is a schematic timing diagram of a;

FIG. 58 is a schematic timing diagram of a;

FIG. 59 is a schematic timing diagram of a;

FIG. 60 is a schematic timing diagram of a;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an apparatus, method and system for providingin a computer system a registered peripheral component interconnect(hereinafter “Registered PCI” or “RegPCI”) bus(es), logic circuitstherefor and signal protocols thereof.

For illustrative purposes, the preferred embodiments of the presentinvention are described hereinafter for computer systems utilizing theIntel x86 microprocessor architecture and certain terms and referenceswill be specific to that processor platform. RegPCI, however, ishardware independent and may be utilized with any host computer designedfor this interface standard. It will be appreciated by those skilled inthe art of computer systems that the present invention may be adaptedand applied to any computer platform utilizing the RegPCI interfacestandard.

Referring to the drawings, the details of preferred embodiments of thepresent invention are schematically illustrated. Like elements in thedrawings will be represented by like numbers, and similar elements willbe represented by like numbers with a different lower case lettersuffix.

Referring to FIG. 1, a schematic block diagram of a computer systemaccording to the present invention is illustrated. The computer systemis generally indicated by the numeral 100 and comprises a centralprocessing unit(s) (“CPU”) 102, core logic 104, system random accessmemory (“RAM”) 106, a video graphics controller 110, a local framebuffer 108, a video display 112, a RegPCI/SCSI bus adapter 114, aRegPCI/EISA/ISA bridge 116, a PCI/IDE controller 118, and, optionally, anetwork interface card (“NIC”) 122. Single or multilevel cache memory(not illustrated) may also be included in the computer system 100according to the current art of microprocessor computer systems. The CPU102 may be a plurality of CPUs 102 in a symmetric or asymmetricmulti-processor configuration.

The CPU(s) 102 is connected to the core logic 104 through a CPU host bus103. The system RAM 106 is connected to the core logic 104 through amemory bus 105. The core logic 104 includes a host-to-PCI bridge betweenthe host bus 103, the memory bus 105 and a RegPCI bus 109. More than oneRegPCI bus is contemplate herein as well as RegPCI-to-RegPCI bridges(not illustrated), and is within the scope and intent of the presentinvention. The local frame buffer 108 is connected between the videographics controller 110 and the RegPCI bus 109. The RegPCI/SCSI busadapter 114, RegPCI/EISA/ISA bridge 116, RegPCI/IDE controller 118 andthe NIC 122 are connected to the REgPCI bus 109. Some of the REgPCIdevices such as the Video controller 110 and NIC 122 may plug into PCIconnectors on the computer system 100 motherboard (FIG. 2).

Hard disk 130 and tape drive 132 are connected to the RegPCI/SCSI busadapter 114 through a SCSI bus 111. The NIC 122 may be connected to alocal area network 119. The RegPCI/EISA/ISA bridge 116 connects over anEISA/ISA bus 113 to a ROM BIOS 140, non-volatile random access memory(NVRAM) 142, modem 120, and input-output controller 126. The modem 120connects to a telephone line 121. The input-output controller 126interfaces with a keyboard 146, real time clock (RTC) 144, mouse 148,floppy disk drive (“FDD”) 150, serial port 152, and parallel port 154.The EISA/ISA bus 113 is a slower information bus than the RegPCI bus109, but it costs less to interface with the EISA/ISA bus 113.

When the computer system 100 is first turned on, start-up informationstored in the ROM BIOS 140 is used to begin operation thereof. Basicsetup instructions are stored in the ROM BIOS 140 so that the computersystem 100 can load more complex operating system software from a memorystorage device such as the disk 130. Before the operating systemsoftware can be loaded, however, certain hardware in the computer system100 shall be configured to properly transfer information from the disk130 to the CPU 102. In the computer system 100 illustrated in FIG. 1,the RegPCI/SCSI bus adapter 114 shall be configured to respond tocommands from the CPU 102 over the RegPCI bus 109 and transferinformation from the disk 130 to the CPU 102 via buses 109 and 103. TheRegPCI/SCSI bus adapter 114 is a RegPCI device and remains platformindependent. Therefore, separate hardware independent commands are usedto setup and control any RegPCI device in the computer system 100. Thesehardware independent commands, however, are located in a RegPCI BIOScontained in the computer system ROM BIOS 140. The RegPCI BIOS isfirmware that is hardware specific but meets the general PCIspecification incorporated by reference herein. Plug and play, and PCIdevices (both PCI and RegPCI) in the computer system are detected andconfigured when a system configuration program is executed. The resultsof the plug and play, and RegPCI device configurations are stored in theNVRAM 142 for later use by the startup programs in the ROM BIOS 140 andPCI BIOS which configure the necessary computer system 100 devicesduring startup. Also during startup a “built-in-self-test” (BIST) may dodiagnostic testing of components, such as RegPCI devices, in thecomputer system.

Referring now to FIG. 2, a schematic diagram of a computer systemmotherboard according to FIG. 1 is illustrated in plan view. Thecomputer system motherboard 200 comprises printed circuit board 202, onwhich components and connectors are mounted thereto. The printed circuitboard 202 comprises conductive printed wiring which is used tointerconnect the components and connectors thereon. The conductiveprinted wiring (illustrated as buses 103, 105 and 109) may be arrangedinto signal buses having controlled impedance characteristics.Illustrated on the printed circuit board are the core logic 104, CPU(s)102, RAM 106, embedded RegPCI/ISA/EISA bridge 116, ISA/EISA connectors312, embedded RegPCI/SCSI bus adapter 114, and PCI connectors 206 a, 206b. The motherboard 200 may be assembled into a case with a power supply,disk drives, etc., (not illustrated) which comprise the computer system100 of FIG. 1.

According to the present invention, Registered PCI introduces severalmajor enhancements to the PCI Specification as follows:

1. Higher clock frequencies such as, for example, 133 MHz.

2. Signaling protocol changes to enable registered outputs and inputs,that is, device outputs that are clocked directly out of a register anddevice inputs that are clocked directly into a register. Signalswitching is generally restricted such that devices can signal 2 clocksbefore an expected response from other devices with the least impact tobus performance.

3. New information passed with each transaction that enables moreefficient buffer management schemes.

-   -   Each new transaction identifies the total number of bytes that        will be read or written, even if the transaction is disconnected        and continued later.    -   Each transaction includes the identity of the initiator        (Initiator Number), the initiator's bus segment (Bus Number) and        transaction sequence (or “thread”) to which it belongs (Sequence        Number).    -   An extended command field further qualifies each transaction.

4. Restricted wait state and disconnection rules optimized for moreefficient use of the bus and memory resources. For example:

-   -   Initiators are not permitted to insert wait states.    -   Targets are not permitted to insert wait states after the        initial data phase.    -   Both initiators and targets are permitted to disconnect        transactions only on naturally aligned boundaries such as, for        example, 128-byte boundaries.

This encourages longer bursts and enables more efficient use ofcacheline-based resources such as the host bus and main memory.

5. Memory read transactions can be completed using Split Transactionprotocol. The target of the transaction terminates the request with aspecial Split Response Termination, executes the command, and initiatesits own Split Completion transaction to send the data back to theoriginal initiator. Initiators are required to support SplitTransactions on all memory reads that use byte-count protocol. A SplitTransaction is a new transaction type, more fully described hereinbelow,that enables memory-read transactions to use the bus almost asefficiently as memory-write transactions. It also enables more efficientdata buffer management by reserving buffer space in the requester ratherthan in the completer of a memory-read transaction. Targets have theoption of supporting Split Transactions.

Each Registered PCI transaction may include, for example but notlimitation, a 4-bit extended command and a 64-bit attribute that carryadditional information about the transaction. This information includes:

-   -   The byte count of an entire initiator operation. An initiator        operation may span multiple bus transactions. The initial        transaction of each operation is marked so the target knows when        to flush buffers containing stale data. Target devices of read        operations can use this information to optimize prefetch and        buffer management algorithms.    -   Initiator and Operation ID. Each initiator identifies its bus        operations (transactions) so complex target devices (such as        host bridges) can optimize their buffer management algorithms to        service individual streams of operations from each master.    -   Split Transaction information. If the initiator requests a long        read from memory and the target is capable of splitting the        transaction, the target will terminate the transaction in a        special way, fetch the requested read data, and initiate its own        Split Completion transaction to transfer the data back to the        original initiator. Split transactions are optional on all other        transactions except memory writes, which are posted.

The disclosure of the present invention includes a detailedspecification of the Registered PCI enhancements to the PCI Local Bus asspecified in the PCI Specification, Revision 2.1 incorporated byreference herein. The PCI specification Rev. 2.1 is available from thePCI Special Interest Group, 2575 NE Kathryn St #17, Hillsboro, Oreg.97124. Requirements of RegPCI that are the same as the conventional PCISpecification, Revision 2.1, are generally not discussed herein.

The following terms and abbreviations disclosed in Table I below aregenerally used hereinafter. TABLE 1 Terms and Abbreviations AllowableThe initiator and target are permitted to disconnect byte-countDisconnect transactions only on naturally aligned 128-byte boundariescalled Boundary (ADB) Allowable Disconnect Boundaries. attribute The64-bit field asserted on AD[63:0] during the attribute phase of aRegistered PCI transaction. Used for further definition of thetransaction. byte-count A memory-read or memory-write transaction usinga byte-countextended transaction command. As the name implies,byte-count transactions use the byte- count field in the attributes. Thebyteenable bus is reserved during byte- count transactions. Byte-counttransactions contain one or more data phases, and FRAME# remainsasserted after IRDY# asserts. The target of a byte-count memory-readtransaction shall complete it in one of five ways: Retry (temporarily),immediate completion, Delayed Transaction, Split Transaction, or TargetAbort. The target of a byte- count memory-write transaction is permittedto complete it in one of three ways: Retry (temporarily) immediatecompletion (posting), or Target Abort. Byte-count transactions shalladdress prefetchable memory locations. byte-enable A transaction thatuses a byte-enable extended command. Byte-enable transactiontransactions are limited to 32-bit data transfers. Transactions usingthe Configuration Read, Configuration Write, I/O Read and I/O Writecommands always use the Byte Enable extended command. Transactions usingMemory Read and Memory Write commands optionally use a byte- enableextended command if the transaction affects only a single DWORD. As thename implies, byte-enable transactions use the byte enable bus tocontrol addressing within a single DWORD. The byte-count field in theattributes is reserved during byte-enable transactions. Byte-enabletransactions always contain a single data phase, and FRAME# alwaysdeasserts when IRDY# asserts. The target of all byte-enable transactionexcept memory writes shall complete the transaction in one of four ways:Retry (temporarily), immediate completion, Delayed Transaction, orTarget-Abort. The target of a byte-enable memory-write transaction ispermitted to complete it in one of three ways: Retry (temporarily),immediate completion (posting), or Target-Abort. Byte-enabletransactions may not be completed as Split Transactions. completer Thetarget of a byte-count memory read transaction that is terminated with aSplit Response. The completer becomes the initiator of the subsequentSplit Completion. A PCI-to-PCI bridge that uses Split Transactions toforward a byte-count memory read acts as a completer on the originatingbus and a requester on the destination bus. device A component of a PCIsystem that connects to a PCI bus. As defined by the PCI Specification,a device can be a single function or a multifunction device. All devicesshall be capable of responding as a target to some transactions on thebus. Many devices are also capable of initiating transactions on thebus. All Registered PCI devices shall support the 64-bit AD bus.extended The 4-bit field asserted on C/BE#[3:0] during the attributephase of a command Registered PCI transaction. This is used for furtherqualification of the type of command the initiator is attempting.initiator A device that initiates a transaction on the bus by requestingthe bus, asserting FRAME#, and asserting the command and address. Abridge forwarding a transaction will be an initiator on the destinationbus. Sequence One or more transactions that result from a singlebyte-count transaction being disconnected (either by the initiator ortarget) and later continued. The initiator marks the first transactionof a Sequence by setting the Initial Sequence Request attribute bit.Each transaction in the same Sequence carries the same Sequence ID. Datafor an entire read Sequence are guaranteed to be valid at the time theinitiator issues the original byte-count memory-read transaction.Hardware buffer management algorithms are permitted to prefetch readdata up to the byte count and hold it indefinitely (not flush buffers)until accepted by the initiator. (See Transaction Sequences hereinbelowfor more details.) Sequence ID The combination of the Initiator BusNumber, Initiator Number, and Sequence Number attributes. Thiscombination uniquely identifies a transaction that resulted from thedisconnection of a single byte-count transaction. Used inbuffer-management algorithms and some ordering rules. requesterInitiator of a byte-count memory read transaction that is terminatedwith a Split Response. The requester becomes the target of thesubsequent Split Completion. When servicing a Split Transactions aPCI-to-PCI bridge acts as a completer on the originating bus and arequester on the destination bus. Split Completion When used in thecontext of the bus protocol, this term refers to a special transaction,by which the completer writes the requested data back to the requester.The Split Completion begins with the same address, command, attributes,and byte count as the corresponding Split Request, and changes theextended command to Split Completion. The completer is permitted to setor clear the Disconnect on First ADB attribute bit, regardless of thestate of the bit in the Split Request. If the Split Completion isdisconnected before the byte count is satisfied, the completer adjuststhe address and byte count for the data already transferred, when theSplit Completion continues. When used in the context of transactionordering and the transaction queues inside the requester and completer,the term refers to a queue entry corresponding to a Split Completiontransaction on the bus. Split Request When used in the context of thebus protocol, this term refers to a byte- count memory read transactionterminated with a Split Response. When used in the context oftransaction ordering and the transaction queues inside the requester andcompleter, the term refers to a queue entry corresponding to a SplitRequest transaction on the bus. When the completer executes the SplitRequest it becomes a Split Completion. Split Response Special protocolfor terminating a byte-count memory read transaction, whereby the targetindicates that it will complete the transaction as a Split Transaction.Split Transaction: A byte-count memory read transaction terminated bythe target with a Split Response, and later completed with a SplitCompletion. target A device that responds to bus transactions. A bridgeforwarding a transaction will be the target on the originating bus.transaction A single sequence of address and data phases associated witha single assertion of FRAME#.

Transaction Comparison Between Registered PCI and Conventional PCI

Referring now to FIGS. 3 and 4, a typical conventional PCI writetransaction (FIG. 3) and a typical Registered PCI write transaction(FIG. 4) are compared. Both FIGS. 3 and 4 illustrate a write transactionwith identical device selection timing and wait states, and six dataphases.

FIG. 3 illustrates a typical conventional PCI write transaction with sixdata phases. The initiator and target do not insert any wait states, andthe transaction completes in 9 clocks, including the bus turn-around.Table 2 lists the phase definitions for the conventional PCI bustransactions as illustrated in FIG. 3. TABLE 2 Conventional PCI BusTransactions Phase Definitions Conventional PCI Phases DescriptionAddress & 1 clock for SAC, 2 clocks for DAC. Command Phase Data PhaseThe clocks (after the address phase) where data transfer takes place.Turn-Around Idle clock for changing from one bus owner to another.

FIG. 4 illustrates a Registered PCI write transaction with six dataphases, according to the present invention. The initiator and target donot insert wait states, and the transaction completes in 10 clocks,including the bus turn-around. FIGS. 3 and 4 illustrate the similaritiesbetween conventional PCI and Registered PCI. The protocol differenceshave been kept to a minimum to lessen the effect of the change ondesigns and on tools for designing and debugging.

FIGS. 3 and 4 also illustrate the effect of Registered PCI protocol onthe length of the transaction. Both transactions show the targetresponding by asserting DEVSEL# two clocks after FRAME# and moving atotal of six data phases. The transaction takes 9 clocks forconventional PCI and 10 clocks for Registered PCI. Table 3 lists thetransaction phases of Registered PCI as illustrated in FIG. 4. TABLE 3Registered PCI Bus Transactions Phase Definitions Registered PCITransaction Phases Description Address Phase 1 clock. See Bus Widthhereinbelow for dual address support in Registered PCI Attribute Phase 1clock phase. This phase is required for all Registered PCI transactionsand is used for further qualification of the type of transaction inprogress. Target Response 1 or more clock phases when the target claimsthe Phase transaction by asserting DEVSEL# (also used but not named inconventional PCI). Data Phase The clock phases where data transfer takesplace. Once the Target Response Phase has been negotiated and datatransfer starts, data is transferred until either the byte count issatisfied or either the target or the initiator signalsDisconnect-with-data to terminate the transaction early. Turn-AroundIdle clock between transactions for changing from one bus driver toanother.

Registered PCI Transaction Protocol

According to the present invention, Registered PCI includes two basictransaction types, byte-enable transactions and byte-count transactions.Byte-enable transactions are limited to a 5 single data phase, use theAD bus during the address phase and the byte enable bus during the dataphase to control which bytes in the AD bus are part of the transaction.The initiator always deasserts FRAME# and asserts IRDY# one clock afterthe attribute phase for byte-enable transactions.

Byte-count transactions include one or more data phases and use theaddress bus during the address phase and byte count during the attributephase to control which bytes in the AD bus are part of the transaction.The initiator leaves FRAME# asserted and asserts IRDY# one clock afterthe attribute phase for byte-count transactions.

Only memory transactions use byte-count transactions. All othertransactions shall use byte-enable rules. Table 4 lists performanceenhancements of byte-count transactions compared to byte-enabletransactions. TABLE 4 Comparison of Byte-Count Transactions overByte-Enable Transactions Byte Count Byte Enable Starting addressspecified on AD bus down to Starting address a byte address (includesAD[2:0]). specified on AD bus down to a byte address (includes AD[2:0]).Supports only sequential burst order. Supports only single data phasetransactions. Byte count in the attribute field determines Byte enablesidentify how many bytes to transfer. Byte enable bus which bytes totransfer is not used (reserved) during data phases. All (same asconventional bytes from the starting address through the PCI). bytecount shall be transferred. The initiator shall permit memory-read SplitTransactions transactions to be completed as a Split not allowed.Transaction. (Optional for targets.) 64-bit data transfers 32-bit datatransfers Memory commands only All commands

Transaction Sequences

A Sequence is one or more transactions that result from a singlebyte-count transaction being disconnected (either by the initiator ortarget) and later continued. Both the target and the initiator arepermitted to disconnect a byte-count transaction, resulting in its beingbroken into multiple transactions. (See Allowable Disconnect Boundaries(ADB) and Buffer Size hereinbelow.) When the initiator begins a newSequence, it sets the Initial Sequence Request attribute in the firsttransaction.

Each transaction in the same Sequence carries the same unique SequenceID (i.e. same Initiator Number, Initiator Bus Number, and SequenceNumber). If an initiator issues a second byte-count memory-readtransaction before a previous one has been completed, the initiator isrequired to use a different Sequence Number. (The target might terminateany byte-count memory-read transaction with Split Response and completethe transaction as a Split Transaction.) Data for an entire readSequence are guaranteed to be valid at the time the initiator issues theoriginal byte-count memory-read transaction. If a target uses DelayedTransactions to execute a byte-count memory read transaction, thetargets hardware buffer management algorithms are permitted to prefetchread data up to the byte count and hold it indefinitely (not flushbuffers) until accepted by the initiator. (See Allowable DisconnectBoundaries (ADB) and Buffer Size hereinbelow for more details.)Registered PCI initiators are required to repeat transactions terminatedwith Retry until the entire byte count is taken. An initiator cannot bereset by its device driver if an incomplete Sequence is outstanding.

Allowable Disconnect Boundaries (ADB) and Buffer Size

Registered PCI defines an Allowable Disconnect Boundary (ADB) as anaturally aligned 128-byte address; that is, an address whose lower 7bits are zeros. After a byte-count data transfer starts, it can only bestopped in one of the following ways: a target or initiatordisconnection at an ADB, or the transaction byte count is satisfied.

If a device operation is prematurely disconnected (that is, atransaction stops on an ADB before moving the entire requested bytecount), a subsequent transaction shall be generated to complete thedevice operation. (A subsequent transaction is a transaction with theInitial Sequence Request bit, AD Bus Bit Postion AD[0]) cleared in theattribute field, more fully described in the Registered PCI Attributeshereinbelow.)

Registered PCI protocol allows a transaction to start on any byteaddress. Both the initiator and the target are permitted to disconnect abyte-count transaction on any ADB. Therefore the minimum buffer sizethat both the initiator and target shall use is 128 bytes. Less data maybe transferred on any particular transaction if the starting address isbetween two ADBs, or if the byte count is satisfied between two ADBs.

Wait States

Registered PCI initiators are not permitted to insert wait states on anydata phase. Registered PCI targets are permitted to insert initial waitstates in pairs of clocks (up to a maximum). No wait states are allowedon subsequent data phases. See **Wait States hereinbelow for details.

Addressing, Byte Enables, and Alignment

Registered PCI allows transactions to begin and end on any byte address.As in conventional PCI, transactions are naturally aligned to bytelanes. That is, any address for which AD[2:0] is 0 uses byte lane 0. Anyaddress for which AD[2:0] is 1 uses byte lane 1, etc.

Byte-enable transactions are similar to conventional PCI in that thebyte enables indicate which bytes in the AD bus are included in thetransactions. Like conventional PCI I/O transactions, the AD bus(including AD[1:0]) for all byte-enable transactions address thestarting byte of the transaction.

For byte-count transactions the initiator uses the full address bus toindicate the starting byte address (including AD[2:0]). The initiatoralso includes the Operation Byte Count in the attribute field. The byteenables are reserved and deasserted (logic level high) throughout abyte-count transaction. All bytes from the starting address through theend of the byte count are included in the transaction or subsequentcontinuations of the transaction. (The byte count will sometimes spanmore that one transaction. See Registered PCI Attributes hereinbelow.)

Split Transactions

Split Transactions enable byte-count memory-read transactions to use thebus almost as efficiently as byte-count memory-write transactions.Byte-count memory-read transactions are the only transactions that canbe completed using Split Transactions. Byte-count memory-writetransactions are posted. Byte-enable transactions cannot be split; theyuse Delayed Transactions (if not completed immediately).

A Split Transaction starts when an initiator (called the requester)initiates a memory-read transaction (called the Split Request) using thea byte-count extended command. If a target that supports SplitTransactions (called the completer) is addressed by such a transaction,it signals a Split Response termination by using a special signalinghandshake more fully described under Split Response Terminationhereinbelow. The completer then fetches the number of bytes specified bythe byte count in the Split Request, or fetches up to a convenient ADBbefore reaching the byte count. The completer then asserts its REQ#signal to request the bus. When the arbiter asserts GNT# to thecompleter, the completer initiates a Split Completion transaction tosend the requested read data to the requester. Notice that for a SplitCompletion transaction the requester and the completer switch roles. Thecompleter becomes the initiator of the Split Completion transaction, andthe requester becomes the target.

Bus Width

According to the present invention, all Registered PCI devices arerequired to support the 64-bit address and data bus. However, it iscontemplated and within the scope of the present invention to implementand support the 32-bit address and data bus.

Conventional PCI includes requirements to enable 32-bit and 64-bitdevices to operate together. Since Registered PCI devices shall operateas conventional devices when installed in conventional systems, and tominimize changes when converting a conventional PCI design to RegisteredPCI, most of the bus-width rules are the same for conventional andRegistered PCI.

For example, only memory transactions use 64-bit data transfers. Allother transactions use 32-bit data transfers.

Requirements stated herein generally assume all devices support a 64-bitbus. It is contemplated and within the scope of the invention, as morefully disclosed under **Bus Width hereinbelow, that 32-bit extensions tothe Registered PCI specification could be incorporated into ftheinvention for example, more cost-sensitive applications. Registered PCIdevices not needing interoperability with future 32-bit devices needriot comply with the requirements described under **Bus Width.

Source Sampling

Like conventional PCI, Registered PCI devices are not permitted to driveand receive the same bus signal at the same time. Registered PCIrequires the designer to insert a means for multiplexing on the inputpath for any signal that the device needs to monitor while the device isdriving the signal. This multiplexing means shall receive on one inputthe registered input signal from the input-output (I/O) connection, andon the other an internal equivalent of the signal being sourced onto thebus with the proper registered delays. The multiplexing means controlshall then be a registered delayed version of the output enable or asourcing flag which will automatically switch the multiplexing means touse the internal equivalent net.

Compatibility and System Initialization

Registered PCI devices operate in conventional or Registered PCI modedepending on the state of DEVSEL# at the rising edge of RST#, as morefully described in Compatibility and System Initialization hereinbelow.If DEVSEL# is deasserted at the rising edge of RST#, the device shalloperate in conventional mode. If DEVSEL# is asserted at the rising edgeof RST#, the device shall operate in Registered PCI mode.

The source bridge for each bus and the pull-up resistor on DEVSEL#provided by the central resource determine the state of DEVSEL# duringRST#. The host bridge that begins a PCI bus hierarchy and a PCI-to-PCIbridge that extends it have slightly different requirements, and aredescribed in Frequency and Mode Initialization Sequence in a HostBridge, and Frequency and Mode Initialization Sequence in a PCI-to-PCIBridge, respectively, hereinbelow.

Summary of Protocol Rules

Protocol rules, according to the present invention, may be divided intothe following categories: basic initiator rules, basic target rules, busarbitration rules, configuration transaction rules, parity error rulesand bus width rules. The following summarizes the protocol rules forRegistered PCI transactions. A more detailed desciption of these ruleswill be made hereinbelow.

Basic Initiator Rules

The following rules control the way a device initiates a transaction.

1. As in conventional PCI protocol, an initiator begins a transaction byasserting FRAME#. The first clock in which FRAME# is asserted is theaddress and command phase. (See Address Width hereinbelow for dualaddress cycles.)

2. There are no address alignment requirements for beginning aRegistered PCI transaction (both byte-count and byte-enabletransactions).

3. The attribute phase clock follows the address phase. The attributesinclude information useful for data-buffer management by the target.

4. Initiator wait states are not permitted. The initiator shall assertIRDY# one clock after the attribute phase. The initiator shall notdeassert IRDY# until the end of the transaction or at an ADB boundary.Therefore, data stepping is not possible on write transactions.

5. For write transactions, the initiator shall assert write data on theAD bus no later than 1 clock after it asserts IRDY#.

6. If the transaction is a byte-enable transaction (that is, if it usesan extended command that is designated for byte-enable transactions),the initiator intends to transfer data in only a single data phase.During the address phase the full AD bus indicates the starting byteaddress of the transaction. The initiator deasserts FRAME# when itasserts IRDY# and uses the byte enables to indicate which bytes of theAD bus are affected by the transaction. (The Operation Byte Count fieldis reserved.) Byte enables shall be asserted 1 clock after the attributephase for both reads and writes. Byte-enable transactions are limited to32-bit data phases.

7. If the transaction is a byte-count transaction (that is, if it usesan extended command that is designated for byte-count transactions), thefollowing rules apply:

-   -   a. The transaction address a prefetchable memory location.    -   b. The AD bus specifies the starting byte address of the        transaction (including AD[2:0]).    -   c. The byte count for the operation is included in the attribute        field.    -   d. Byte enables are reserved and deasserted (high logic voltage)        throughout the transaction. All bytes are included in the        transaction from the starting address through the byte count.    -   e. The initiator keeps FRAME# asserted after it asserts IRDY#.    -   f. The initiator is limited to terminating the transaction only        on naturally aligned 128-byte boundaries called Allowable        Disconnect Boundaries (unless the byte count is satisfied        sooner).    -   g. A transaction will have less than 4 data phases in the        following two cases: 1) The byte count is satisfied in less than        4 data phases, or 2) The transaction starts less than 4 data        phases from an ADB and the Disconnect on ADB attribute bit is        set. In both of these cases the initiator shall deassert FRAME#        two clock after TRDY# asserts for transactions with 3 data        phases. If the transaction has 2 or 1 data phases the initiator        shall deassert FRAME# with the IRDY# deassertion. If the        transaction has 3 or 2 data phases, the initiator shall deassert        IRDY# one clock after the last data phase. If the transaction        has 1 data phase, the initiator shall deassert IRDY# 2 clocks        after the data phase.    -   h. If the byte-count transaction requires 4 or more data phases,        the initiator shall terminate the transfer when the byte count        is satisfied. The initiator is also permitted to terminate the        transaction on any ADB. To terminate the transfer, the initiator        deasserts FRAME# 1 clock before the last data phase (the last        data phase is the clock in which the byte count is satisfied, or        the last data phase before crossing the ADB), and deasserts        IRDY# 1 clock after the last data phase.    -   i. If the target asserts STOP# 4 clocks before an ADB, the        initiator will deassert FRAME# 2 clocks later, and terminate the        transaction on the ADB.    -   j. If the transaction is a write and the target inserts wait        states, the initiator shall toggle between its first and second        data transfers until the target asserts TRDY#.

8. A Registered PCI initiator is required to repeat all transactionsterminated with Retry. There is no exception (as in conventional PCI)for the device being reset. The device driver is not permitted to resetthe device, if the device has issued a request that was terminated withRetry or Split Response and that request has not completed (entire bytecount transferred).

9. Like conventional PCI, no device is permitted to drive and receive abus signal at the same time.

Basic Target Rules

The present invention applies the following rules to the way a targetresponds to a transaction.

1. The target claims the transaction by asserting DEVSEL# using timingA, B, C or SUB, as given in Table 5 hereinbelow. Conventional DEVSEL#timing is included for reference. TABLE 5 Registered PCI DEVSEL# TimingDecode Speed Registered PCI Conventional PCI 1 clock after address NotSupported Fast 2 clocks after address Decode A Medium 3 clocks afteraddress Decode B Slow 4 clocks after address Decode C SUB 6 clocks afteraddress SUB N/A

2. The target asserts TRDY# an odd number of clocks after it assertsDEVSEL#. The target cannot deassert TRDY# until the end of thetransaction. Target wait states are not permitted after the initial dataphase. Therefore, data stepping is not possible after the first dataphase of read transactions.

3. A Registered PCI target is required to meet the same target initiallatency requirements as a conventional target. That is, the target shallassert TRDY# or STOP# within 16 clocks from the assertion of FRAME#.Host bridges are allowed to extended this time in some cases. See **WaitStates hereinbelow for details.

4. If the transaction uses a byte-enable extended command, the targetshall assert TRDY# an odd number of clocks after it asserts DEVSEL#, anddeassert TRDY# and DEVSEL# together one clock later.

5. Targets shall alias reserved command encoding 1100 b to Memory Readand 1111 b to Memory Write.

6. If the transaction uses a byte-count extended command, the followingrules apply:

-   -   a. The target is limited to terminating the transaction only on        naturally aligned 128-byte boundaries called Allowable        Disconnect Boundaries (ADB) (unless the byte count is satisfied        sooner).    -   b. If the byte count is satisfied, the target deasserts TRDY# on        the clock after the last data phase of the transaction.    -   c. To terminate the transaction on an ADB after 4 or more data        phases the target asserts STOP# 1 clock before the last data        phase (i.e. 2 clocks before crossing the ADB), and deasserts        TRDY# and STOP# 1 clock after the last data phase.    -   d. If the transaction starts 1, 2, or 3 data phases from an ADB,        and the target wants to disconnect the transaction on the ADB,        the target asserts STOP# when it asserts TRDY#. The target then        deasserts STOP# when it deasserts TRDY#.

7. If the transaction is one of the special termination cases that donot transfer data, the target shall assert and deassert DEVSEL#, TRDY#and STOP# according to the following cases:

-   -   a. Target-Abort on the first data phase—The target deasserts        DEVSEL# and asserts STOP# together an odd number of clocks after        it asserts DEVSEL#. The target deasserts STOP# 1 clock later.        TRDY# is not asserted.    -   b. Retry termination—The target asserts STOP# an odd number of        clocks after it asserts DEVSEL#. The target deasserts STOP# and        DEVSEL# 1 clock later. TRDY# is not asserted.    -   c. Split Response termination—The target asserts STOP# an odd        number of clocks after it asserts DEVSEL#, and asserts TRDY# one        clock later with all bits on the AD bus driven high. The target        deasserts STOP#, DEVSEL#, and TRDY# together 1 clock after it        asserts TRDY#.

8. Like conventional PCI, no device is permitted to drive and receive abus signal at the same time.

9. Prefetchable memory address ranges for all devices are no smallerthan 128 bytes. If an initiator issues a byte-count memory-read to adevice starting at an implemented address and proceeding to the nextADB, the device shall return FFh for each unimplemented byte.

Bus Arbitration Rules

According to the present invention, the following protocol rules applyto bus arbitration.

1. All REQ# and GNT# signals are registered by the arbiter as well as byall initiators.

2. An initiator is permitted to start a new transaction (drive the ADbus, etc.) on any clock N in which the initiator's GNT# was asserted onclock N−2, and any of the following three conditions is true:

-   -   a) The bus was idle (FRAME# and IRDY# were both deasserted) on        clock N−2.    -   b) The previous transaction was a byte-count transaction, and        FRAME# was deasserted on clock N−3.    -   c) The previous transaction was a byte-enable transaction, the        command was not a reserved command, and TRDY# or STOP# was        asserted on clock N−3.

3. An initiator is permitted to start a new transaction on clock N evenif GNT# is deasserted on clock N−1 (assuming the requirements of item 2above are met).

4. An initiator is permitted to assert and deassert REQ# on any clock.There is no requirement to deassert REQ# after a target termination(STOP# asserted). The arbiter is assumed to monitor bus transactions todetermine when a transaction has been target terminated.

5. If all the GNT# signals are deasserted, the arbiter is permitted toassert any GNT# on any clock. After the arbiter asserts GNT# the arbitercan deassert it on any clock. However, the arbiter shall fairly provideopportunities for all devices to execute Configuration transactions,which require GNT# to remain asserted for a minimum of five clocks whilethe bus is idle.

6. If the arbiter deasserts GNT# to one device, it cannot assert GNT# toanother device until the next clock.

Configuration Transaction Rules

The following protocol rules apply to Configuration transactions.

1. Registered PCI initiators shall provide 4 clocks of address steppingfor Configuration transactions when in Registered PCI mode.

Parity Error Rules

The following protocol rules apply to exception conditions.

1. If a device receiving data detects a data parity error, it shallassert PERR# on the second clock after PAR is asserted (1 clock laterthan conventional PCI).

2. During read transactions the target drives PAR on clock N+1 for theread-data it drove on clock N and the byte enables driven by theinitiator on clock N−1.

3. All Registered PCI device adapters are required to service PERR#conditions for their transactions. See the section titled “ErrorHandling and Fault Tolerance.”

4. Whether a device decodes it address during the address phase or not,if that device detects a parity error on an attribute phase, the deviceasserts SERR#. Other SERR# and status bit requirements for address-phaseand data-phase errors are the same as for conventional PCI.

Bus Width Rules

Preferrably, all Registered PCI devices shall have a 64-bit address/data(AD) bus. However, it contemplated in this specification and within thescope of the invention to also include 32-bit devices.

The width of the address is independent of the width of the datatransfer. All Registered PCI addresses are 64 bits wide (even for 32-bitembodiments of the devices). New registers are defined for RegisteredPCI-to-PCI bridges to extend the non-prefetchable memory base and limitregisters to 64 bits. (See Memory Base Upper 32-Bits and Memory LimitUpper 32-Bits hereinbelow.) The address phase is generally a singleclock long. A new configuration bit is defined for interoperability withfuture 32-bit devices. If this bit is set and the address is greaterthan 4 GB, the initiator will use a dual address cycle (likeconventional PCI) on all transactions.

The attribute phase is always a single clock long. A configuration bitis defined for interoperability with future 32-bit devices. If this bitis set, the upper 32-bits of the attributes are ignored and assumed tobe zero by 64-bit devices.

Only byte-count transactions (memory-read or memory-write) use 64-bitdata transfers. (This maximizes similarity with conventional PCI, inwhich only memory transactions use 64-bit data transfers.) The width ofeach transaction is determined with a handshake protocol on REQ64# andACK64#, just like conventional PCI.

Registered PCI Command Encoding

Table 6 below compares conventional PCI commands with Registered PCIcommands. Initiators shall not generate reserved commands. Targets shallignore all transactions using a reserved command, except as noted below.TABLE 6 Registered PCI Command Encoding C/BE[3:0]# or ConventionalRegistered PCI C/BE[7:4]# PCI Command Command Notes 0000 InterruptAcknowledge Interrupt Acknowledge 0001 Special Cycles Special Cycles0010 I/O Read I/O Read 0011 I/O Write I/O Write 0100 Reserved Reserved0101 Reserved Reserved 0110 Memory Read Memory Read 0111 Memory WriteMemory Write 1000 Reserved Reserved 1001 Reserved Reserved 1010Configuration Read Configuration Read 1011 Configuration WriteConfiguration Write 1100 Memory Read Multiple Reserved, Alias to 2Memory Read 1101 Dual Address Cycle Dual Address Cycle 1110 Memory ReadLine Reserved 1111 Memory Write and Reserved, Alias to 3 InvalidateMemory WriteNotes:1. The actual transaction command appears on C/BE[7:4]# only forbyte-count memory transactions that have an address greater than 4 GB.In this case C/BE[3:0]# contains the Dual Address Cycle command. For allother transactions the actual command appears on C/BE[3:0]#.2. This command is reserved for use in future versions of thisspecification. Current initiators shall not generate this command.Current target shall treat this command as if it were Memory Read.3. This command is reserved for use in future versions of thisspecification. Current initiators shall not generate this command.Current target shall treat this command as if it were Memory Write.

Registered PCI Extended Command Encoding

Table 7 lists Registered PCI command types. TABLE 7 Registered PCIExtended Command Encoding Transaction Extended C/BE[3:0]# Type CommandType Extended Command 0000 Byte enable Validated Reserved 0001 Byteenable Validated Reserved 0010 Byte enable Validated Reserved 0011 Byteenable Validated Split Completion Exception Message 0100 Byte enableImmediate Reserved 0101 Byte enable Immediate Reserved 0110 Byte enableImmediate Reserved 0111 Byte enable Immediate Standard Byte-EnableExtended Command 1000 Byte count Validated Reserved 1001 Byte countValidated Reserved 1010 Byte count Validated Reserved 1011 Byte countValidated Split Completion 1100 Byte count Immediate Reserved 1101 Bytecount Immediate Reserved 1110 Byte count Immediate Reserved 1111 Bytecount Immediate Standard Byte-Count Extended Command

The extended command is used to qualify the type of transaction andattributes being used by the initiator. The extended command appears onC/BE[3:0]# of the attribute phase for all transactions. C/BE[7:4]# arereserved during the attribute phase and driven to a high logic voltageby the initiator.

The extended commands are divided into four groups based on thetransaction type and extended command type. Transactions are eitherbyte-count or byte-enable transaction types and are described in moredetail under Byte-Count Transactions and Byte-Enable Transactionshereinbelow.

Extended command types are either validated or immediate. Extendedcommand types define a path for the addition of new extended commands inthe future. They establish the behavior for current devices when theyencounter a reserved extended command. Reserved extended commandencodings can be assigned in the future to new extended commands thatwill behave predictably with current devices.

Validated Extended Command

A Registered PCI target that detects a reserved validated extendedcommand shall terminate the transaction with Target-Abort. Table 8 liststhe validated extended commands comtemplated for the present invention.TABLE 8 Validated Extended Commands Extended Command Description SplitCompletion This is the requested read data being returned as thecompletion of the Split Request. Refer to Split Transactions hereinbelowfor additional details. Split Completion This extended command functionsin a similar Exception Message fashion to a Split Completion extendedcommand. However, instead of carrying the requested completion data orstatus, this extended command is used to communicate the cause of anexception condition that occurred while executing the Split Request.Refer to Split Transactions hereinbelow for additional details.

Immediate Extended Command

A Registered PCI target that detects a reserved immediate extendedcommand shall execute the transaction as if a standard extended commandwere used. If the reserved extended command is a byte-count extendedcommand, the target shall execute the transaction as if the StandardByte-Count Extended Command were used. If the reserved extended commandis a byte-enable extended command, the target shall execute thetransaction as if the Standard Byte-Enable Extended Command were used.It is contemplated herein that initiators will expect targets that donot understand these new extended commands to execute them as if theywere the standard extended command for their transaction type. Table 9lists the Immediate Extended Command definitions. TABLE 9 ImmediateExtended Command Definitions Extended Command Fields DescriptionStandard Byte-Count Extended This is the default extended Commandcommand for byte-count transactions. Standard Byte-Enable Extended Thisis the default extended Command command for byte-enable transactions.

Registered PCI Attributes

The attribute field is a 64-bit field that further defines and describesthe transaction. The attributes appear in the clock following theaddress phase on the AD bus. The following section describes thesupported attribute definitions.

Table 10 lists the bit assignments in the PCI AD bus. TABLE 10 AttributeBit Positions AD Bus Bit Position Attribute Phase Signal Name AD[0]Initial Sequence Request AD[1] Disconnect on first ADB AD[2] RelaxedOrdering AD[3] Don't Snoop AD[8:4] Initiator Bus Number, lower 5 bitsAD[13:9] Initiator Number, lower 5 bits AD[16:14] Sequence Number, lower3 bits AD[26:17] Byte Count, lower 10 bits AD[31:27] Reserved AD[34:32]Initiator Bus Number, upper 3 bits AD[35] Initiator Number, upper 1 bitsAD[36] Sequence Number, upper 1 bits AD[38:37] Byte Count, upper 2 bitsAD[63:39] Reserved

Table 11 describes the bit definitions of the attribute fields. Allreserved bit fields shall be set to 0. TABLE 11 Attribute FieldDefinitions Attribute Function Initial Sequence This bit indicates thatthe current transaction starts a new initiator Request Sequence. If theSequence is divided into multiple transactions as a result of a targetor initiator disconnection, the subsequent transactions will not havethis bit set. 1 - The initiator is starting a new Sequence. 0 - This isnot the start of the new Sequence. This bit is used for transactioncombining and reordering the buffer management. See Transaction SequenceCombining and Re-ordering hereinbelow for more details. RegisteredPCI-to-PCI bridges forward this bit unmodified with the transaction,even if the bit is not used by the bridge. Disconnect on First Aninitiator sets this bit if its buffer management algorithm requires itADB to disconnect a byte-count transaction on reaching the first ADB.The initiator shall set this bit if the transaction starts 1, 2, or 3data phases from the first ADB, and the initiator wants to disconnectthere. The initiator may optionally set this bit if the transactionstarts 4 or more data phases from the ADB and the initiator wants todisconnect there. (In the second case the initiator shall also deassertFRAME# 1 clock before the last data phase.) The bit is needed becausethe initiator is unable to respond fast enough in Registered PCI tonotify the target of a disconnection request stating 1, 2, or 3 dataphase from the first ADB. Relaxed Ordering An initiator sets this bit ona read transaction if its usage model does not require Delayed ReadCompletions or Split Read Completions for this transaction to stay inorder with respect to posted memory writes moving in the same direction.Delayed Read Requests and Split Read Request are unaffected by this bit.An initiator sets this bit on a memory-write transaction if its usagemodel does not require this memory-write transaction to stay in orderwith respect to other memory-write transactions moving in the samedirection. This bit is optional for targets. If the target (or anintervening bridge) implements this bit and the bit is set for a readtransaction, the target is permitted to allow read-completion data topass posted-memory-write transactions moving in the same direction. Ifthe bit is set for a memory-write transaction, the target (orintervening bridge) is permitted to allow this memory-write transactionto pass any previously posted memory-write transactions. If the target(or intervening bridge) does not implement this bit or the bit is notset for a transaction, the target shall adhere to conventional PCIordering rules for this transaction. (See Relaxed Ordering Ruleshereinbelow for a discussion of usage models for transaction ordering.)Registered PCI-to-PCI bridges forward this bit unmodified with thetransaction, even if the bit is not used by the bridge. Don't Snoop Ifan initiator sets this bit, the initiator guarantees that caches do notneed to snoop this transaction. How the initiator guarantees this isbeyond the scope of this specification. Examples of transactions thatcould benefit from setting this bit are transactions that read or writenon-cacheable sections of main memory, or sections that have previouslybeen flushed from the cache through hardware or software means. Notethat Registered PCI does not require systems to support coherent cachesfor addressed accessed by Registered PCI initiators, but for thosesystems that do, this bit allows device drivers to stop cache snoopingon a transaction-by-transaction basis to improve performance. This bitis generally ignored by Registered PCI-to-PCI bridges and forwardedunmodified with the transaction. Initiator Bus Number This 8-bit fieldis divided between the upper and lower halves of the attribute field. Itis used by initiators of Split Transactions to identify the appropriateSplit Completion transaction. It is used by Registered PCI bridges todetermine when to forward a Split Completion. The combination of theInitiator Bus Number, Initiator Number, and Sequence Number is referredto as the Sequence ID. Initiator Number This 6-bit field is dividedbetween the upper and lower halves of the attribute field. For each bussegment system configuration software assigns a unique Initiator Numberto each single-function device and to each function within amultifunction device. Initiators of Split Transactions use it toidentify the appropriate Split Completion transaction. Targetsoptionally use it to optimize buffer management. (See TransactionSequences hereinabove.) The combination of the Initiator Bus Number,Initiator Number, and Sequence Number is referred to as the Sequence ID.Sequence Number This 4-bit field is divided between the upper and lowerhalves of the attribute field. It uniquely identifies up to 16 busoperations from a single initiator. Initiators of Split Transactions useit to identify the appropriate Split Completion transaction. Targetsoptionally use it to optimize buffer management. (See TransactionSequences hereinabove.) The initiator shall assign a unique SequenceNumber to each transaction. How the initiator assign these numbers isnot controlled by this specification. The combination of the InitiatorBus Number, Initiator Number, and Sequence Number is referred to as theSequence ID. Byte Count This 12-bit field is divided between the upperand lower halves of the attribute field. It indicates the number ofbytes the initiator is planning to move in the remainder of thisSequence. There is no guarantee that the initiator will successfullymove the entire byte count in a single transaction. If this transactionis disconnected for any reason, the initiator shall adjust the ByteCount in the subsequent transactions of the same Sequence to be thenumber of bytes remaining in this Sequence. The Byte Count is specifiedas a binary number, with 0000 0000 0001b indicating 1 byte, 1111 11111111b indicating 4095 bytes, and 0000 0000 0000b indicating 4096 bytes.

Byte-Count Transactions

According to the present invention, basic Byte-Count Write andByte-Count Read transactions are described hereinbelow. All figuresillustrate a 64-bit AD bus and 8-bit C/BE# bus. REQ64# and ACK64# arenot illustrated to aid in readablility, however, it is contemplated andwithin the scope of the present invention that REQ64# is asserted by theinitiator with FRAME# assertion and ACK64# is asserted by the targetwith DEVSEL# assertion. See Bus Width Rules hereinabove for more detailson the REQ64# and ACK64# assertions.

Writes

Referring to FIGS. 5 and 6, byte-count write transactions areillustrated. The top portion of FIGS. 5 and 6 illustrate the signals asthey appear on the bus. The middle and lower portions of the figure showthe view of the PCI bus from the initiator and target, respectively.Signal names preceded by “s1_” indicate a signal that is internal to thedevice after the bus signal has been sampled. For example, the initiatorasserts FRAME# on clock 3. The target samples FRAME#, so s1_FRAME# isasserted on clock 4. According to the present invention, the data is notrequired to be valid in the clock after the attribute phase of a writetransaction (and a Split Completion). This clock could be used as aturn-around clock by multi-package host bridges that source the addressfrom one package and the data from another.

FIG. 5 illustrates the minimum target initial latency of 3 clocks. Atclock 5, data is not required to be valid, even with the assertion ofIRDY# by the initiator. FIG. 6 illustrates a similar transaction to theone illustrated in FIG. 5, but with only 6 data phases and a targetinitial latency of 5 clocks. Notice at clocks 6 and 7 the initiatortoggling between DATA0 and DATA1. This toggling starts once theinitiator detects the target assertion of DEVSEL#, and continues untilthe initiator detects the target assertion of TRDY#, which does notoccur until clock 8.

Reads

Referring now to FIGS. 7 and 8, schematic timing diagrams of aByte-Count Memory-Read Transaction with No Target Initial Wait Statesand a Byte-Count Memory-Read Transaction with Target Initial WaitStates, respectively, are illustrated. FIG. 7 illustrates a byte-countread transaction with the minimum target initial latency of 3 clocks.The top portion of the diagram of FIG. 7 illustrates the signals as theyappear on the bus. The middle and lower portions of the diagram of FIG.7 illustrate the view of the PCI bus from the initiator and target,respectively. Signal names preceded by “s1_” indicate a signal that isinternal to the device after the bus signal has been sampled. FIG. 8illustrates a similar transaction to the one illustrated in FIG. 7, butwith only 6 data phases and an initial target latency of 5 clocks.

Byte-Enable Transactions

According to the present invention, the initiator signals its intentionto execute a byte-enable transaction by using a byte-enable extendedcommand. For a byte-enable transaction the initiator deasserts FRAME# onthe clock after the attribute phase (the same time it asserts IRDY#). Aswith byte-count transactions, the target asserts DEVSEL# and then an oddnumber of clocks later it asserts TRDY#. However for a byte-enabletransaction the target leaves TRDY# asserted for only a single clock.The initiator deasserts IRDY# one clock after that.

If the target asserts TRDY# on a byte-enable transaction, the targetdoes not assert STOP#. See Byte-Enable Transactions associated withFigure **(2.13.2.2) and Byte-Enable Transactions associated with Figure**(2.13.5.2) hereinbelow for the use of STOP# in Retry and Target-Aborttermination of byte-enable transaction.

For Byte-Enable transactions, the Byte-Count attribute filed shall betreated as a reserved field, and as such, shall be set to 0.

Writes

Referring to FIG. 9, a schematic timing diagram of a Byte-Enable WriteTransaction with No Wait States illustrates the initiator executing abyte-enable write. In FIG. 9 the target does not insert any wait states,asserting TRDY# on clock 6. As in conventional PCI, data is transferredwhen TRDY#, IRDY#, and DEVSEL# are asserted. However, notice theinitiator continues driving the bus, and IRDY# remains asserted in clock7, even though this is one clock past the single clock in which data wastransferred (clock 6). According to the present invention the RegisteredPCI initiator requires two clocks to respond to the assertion of TRDY#.

Referring to FIG. 10, a schematic timing diagram of a Byte-Enable Readwith Two Target Initial Wait States illustrates an initiator executing abyte-enable read. In FIG. 10 the target inserts two wait states atclocks 6 and 7, then asserts TRDY# for a single clock at clock 8. As inconventional PCI, data is transferred when TRDY#, IRDY#, and DEVSEL# areasserted. However, notice the initiator continues driving the C/BE busand IRDY# remains asserted in clock 9, even though this is one clockpast the single clock in which data was transferred (clock 8).

In an embodiment of the present invention, Byte enables are not validuntil the clock after the attribute phase. Preferrably, Registered PCItargets with non-prefetchable locations shall not start a destructiveread operation until the byte enables are valid. The target mayaccommodate this by inserting 2 target initial wait states for deviceselect assertion A. If the targeted device has a device select of B orslower, then the target requires no initial wait states. FIG. 10illustrates a target with a device select assertion of A inserting 2target initial wait states.

Device Select Timing

Registered PCI targets are required to claims transaction by assertingDEVSEL# using timing A, B, C or SUB, this is done by the targetasserting DEVSEL# on clock 2, 3, 4 or 6 respectively after theinitiator's assertion of FRAME#. The following description hereinbelowillustrates device select timing using four data phase Byte-Count writeand read transactions. Notice that the target assertion of DEVSEL#relative to the initiator's assertion of FRAME# remains the same for alllegal transaction types, in accordance with the Registered PCIinvention.

Writes

Preferrably, a target decode of B with zero initial wait states isfaster than a target decode of A with 2 initial wait states, see **WaitStates hereinbelow for a more detail description on wait state pairs.FIG. 11 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “A” with 0 Initial Wait States. FIG.12 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “B” with 0 Initial Wait States. FIG.13 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “C” with 0 Initial Wait States. FIG.14 is a schematic timing diagram of a Four Data Phase Byte-CountMemory-Write Showing Target Decode “Subtractive” with 0 Initial WaitStates;

Reads

According to the present invention, FIG. 15 is a schematic timingdiagram of a Four Data Phase Byte-Count Memory-Read showing TargetDecode “A” with 0 Initial Wait States. FIG. 16 is a schematic timingdiagram of a Four Data Phase Byte-Count Memory-Read showing TargetDecode “B” with 0 Initial Wait States. FIG. 17 is a schematic timingdiagram of a Four Data Phase Byte-Count Memory-Read showing TargetDecode “C” with 0 Initial Wait States. FIG. 18 is a schematic timingdiagram of a Four Data Phase Byte-Count Memory-Read showing TargetDecode “Subtractive” with 0 Initial Wait States.

Wait States

According to the present invention, Registered PCI initiators do notinsert wait states. Initiators are required to assert IRDY# one clockafter the attribute phase. The initiator shall drive write data andshall be prepared to accept read data one clock after IRDY# is asserted.After IRDY# is asserts it shall remain asserted until the end of thetransaction.

Registered PCI targets are permitted to insert initial wait states inpairs of clocks. The target shall assert TRDY# (or STOP#) an odd numberof clocks after it asserts DEVSEL#. A Registered PCI target shall meetthe same target initial latency requirements as a conventional target.That is, the target shall assert TRDY# (or STOP#) within 16 clocks fromthe assertion of FRAME#. This rule applies to all devices except hostbridges. Host bridges are encouraged to meet the 16 clock target initiallatency on most accesses, but are permitted to extend the target initiallatency up to the limit shown in Table 12 hereinbelow for typicalsituations in which meeting the smaller number is not possible. TABLE 12Target Initial Latency Host-Bridge Operating Device Target TargetInitial Frequency Initial Latency Latency Units  33 MHz (ref) 16 32clocks  66 MHz (ref) 16 32 clocks 100 MHz 16 48 clocks 133 MHz 16 64clocks

After TRDY# is asserted it shall remain asserted until the end of thetransaction. Preferrably, devices should minimize initial latency of thetarget.

Wait states should not be used, but if necessary, the number of waitstates shall be kept to a minimum. Preferrably, terminating thetransaction with Retry or executing it as a Split Transaction willprovide more efficient use of the bus. In many cases the transactionalso completes sooner. The use of Retry and Split Transactions ispreferred unless there is a high probability that inserting target waitstates will be faster. Even in high-frequency systems with few (maybeonly one) slots, Retry termination and Split Transactions allowmulti-threaded devices (e.g. multiple devices behind a PCI-to-PCIbridge) to issue multiple transactions concurrently.

Detailed timing requirements for target initial wait states areillustrated in FIGS. 19-24.

Writes

Referring now to FIGS. 19-21, FIG. 19 illustrates a Four Data PhaseByte-Count Memory-Write Showing Target Decode “A” with 2 Initial WaitStates. FIG. 20 is a schematic timing diagram of a Four Data PhaseByte-Count Memory-Write Showing Target Decode “A” with 4 Initial WaitStates. FIG. 21 is a schematic timing diagram of a Four Data PhaseByte-Count Memory-Write Showing Target Decode “C” with 2 Initial WaitStates.

FIG. 19 illustrates a write transaction with 4 data phases, at clocks 6and 7 the initiator toggling between DATA0 and DATA1. This togglingstarts once the initiator detects the target assertion of DEVSEL#, andcontinues until the initiator detects the target assertion of TRDY#,which does not occur until clock 8. FIG. 20 illustrates a similartransaction with 4 target initial wait states, with the initiatortoggling DATA0 and DATA1 at clocks 6, 7, 8, and 9, until the initiatordetects the targets assertion of TRDY# at clock 10.

Reads

Referring now to FIGS. 22-24, FIG. 22 illustrates a schematic timingdiagram of a Four Data Phase Byte-Count Memory-Read Showing TargetDecode “A” with 2 Initial Wait States. FIG. 23 illustrates a schematictiming diagram of a Four Data Phase Byte-Count Memory-Read ShowingTarget Decode “A” with 4 Initial Wait States. FIG. 24 illustrates aschematic timing diagram of a Four Data Phase Byte-Count Memory-ReadShowing Target Decode “C” with 2 Initial Wait States.

Configuration Transactions

Registered PCI initiators shall provide 4 clocks of valid address beforeasserting FRAME#. This allows time for the IDSEL input signal to risethrough a series resistor on the system board. Once FRAME# is asserted,the rest of the transaction proceeds like any other byte-enabletransaction. FIGS. 25 and 26 illustrate a Registered PCIconfiguration-write transaction and a configuration-read transaction,respectively. Both FIGS. 25 and 26 show DEVSEL# timing A with 2 targetinitial wait states. All legal DEVSEL# timing speeds and initial waitstates combinations are valid for configuration transactions as well.Note that DEVSEL# timing B with no initial wait states is actually oneclock faster the examples shown in FIG. 25 and 26.

Delayed Transactions

Delayed Transactions are contemplated herein and are within the scope ofthe Registered PCI invention, however, the use of Delayed Transactionspreferrably should be minimized. Split Transactions are preferred inplace of Delayed Transactions as a Split Transaction generally providesmore efficient use of the bus, see Split Transactions hereinbelow for amore detailed discription of Split Transactions. In many cases a SplitTransaction also completes sooner in addition to allowing multi-threadeddevices (e.g. multiple devices behind a PCI-to-PCI bridge) to issuemultiple transactions concurrently. If a Delayed Transaction cannot beavoided, the following rules shall apply.

For the initiator:

1. The initiator is shall repeat the full starting address specified onthe AD bus down to the byte, including AD[2:0] for all transactionterminated with Retry.

2. The initiator shall repeat all attributes for all transactionterminated with Retry

3. The initiator shall repeat a transaction terminated with Retry, untilthe transaction completes. Device drivers are not permitted to reset anydevice with an outstanding transaction (either Delayed Transaction orSplit Transaction)

For the target:

1. The target shall latch and compare a Delayed Transaction just likeconventional PCI. Targets are optionally allowed to further identify thetransaction using the Initiator Sequence ID and/or Byte-Count.

2. The target is not required to use the Discard Timer like conventionalPCI since Registered PCI initiators are required to repeat all Retryedtransactions.

Split Transactions

According to the Registered PCI invention, Split Transactions is a new,novel and non-obvious transaction type that enables memory-readtransactions to use the bus almost as efficiently as memory-writetransactions.

Basic Split Transaction Requirements

Only memory-read transactions that use byte-count protocol use SplitTransactions. The target of any byte-count memory-read transaction mayoptionally complete the transaction as a Split Transaction or may useany other termination method (immediate response, Retry, or DelayedTransaction), as determined by the rules for those termination methods.All of these termination alternatives are available regardless ofwhether the transaction was previously terminated with Retry, or whetherthe transaction is the initial transaction of a Sequence (i.e. theInitial Sequence Request attribute bit is set) or a continuation of aSequence previously disconnected after transferring some data. Once thetarget terminates a byte-count memory-read transaction with SplitResponse, the target shall transfer the entire remaining byte count as aSplit Completion (except for error conditions described hereinbelow).

A Split Transaction begins when an initiator (called the requester)initiates a memory-read transaction using a byte-count extended command.If a target (called the completer) that supports Split Transactions isaddressed by such a transaction, it may optionally signal a SplitResponse termination by doing the following:

1. Assert DEVSEL# in the response phase to claim the transaction onclock N.

2. Assert STOP# on clock N+1.

3. Assert TRDY# on clock N+2.

4. Deassert TRDY#, STOP#, and DEVSEL# to terminate the transaction onclock N+3.

The above four-step sequence assumes no target initial waits wereinserted between steps 1 and 2. If target initial wait states wereinserted, steps 2 thru 4 shall be adjusted accordingly.

The completer fetches the byte count specified in the Split Request, orfetches up to a convenient ADB before reaching the byte count. Thecompleter then asserts its REQ# signal to request the bus. When thearbiter asserts GNT# to the completer, the completer initiates a SplitCompletion transaction to send the requested read-data to the requester.Notice that for a Split Completion transaction the requester and thecompleter switch roles. The completer becomes the initiator of the SplitCompletion transaction, and the requester becomes the target.

A Split Completion transaction begins with the same command, address,and attributes (unless otherwise indicated) as the original byte-countmemory-read transaction (the Split Request). The extended command isSplit Completion. The byte count will be the same as the Split Request,except in error conditions described later. The Initial Sequence Requestbit is set when the Split Completion begins. The completer is permittedto set or clear the Disconnect on First ADB attribute bit in the SplitCompletion, regardless of the state of the bit in the Split Request.

The completer and the requester are permitted to disconnect the SplitCompletion transaction on any ADB, following the same protocol as amemory-write transaction. If a Split Completion is disconnected beforeall the requested data is sent, the completer continues to request thebus to send the rest of the data. Note that the Completer might delay asimilar length of time preparing the continuation of the SplitCompletion that it did preparing the first part of the Sequence. Whenthe completer is granted the bus, it continues the Split Completionusing the same Sequence ID but adjusting the address and byte count forthe data already sent, and resetting the Initial Sequence Requestattribute. The completer shall keep all Split Completions for a singleSplit Request (i.e. with the same Sequence ID) in ascending addressorder. An intervening bridge shall maintain the order of SplitCompletion transactions with the same Sequence ID.

Requesters and intervening bridges identify individual Split Completionsby their Initiator Bus Number and Initiator Number. The requester claimsthe transaction and accepts the data, using decode timing B or slower.(The requester shall wait for the Split Completion extended command toarrive before it can determine whether or not to claim the transaction.)A PCI-to-PCI bridge forwards a Split Completion based on the InitiatorBus Number in the attribute field. If the Initiator Bus Number isbetween the bridge's secondary bus number and subordinate bus number,inclusive, the bridge forwards the Split Completion. The bridge ignoresthe address of Split Completions (since the address is that of thecompleter not the requester).

A completer is permitted to accept a single Split Request at a time.Such a device is permitted to terminate subsequent byte-countmemory-read transactions with Retry until the requester accepts theSplit Completion. (Overall system performance will generally be betterif completers accept multiple Split Transactions at the same time.)

Requirements for Accepting Split Completions

The requester shall accept all Split Completions resulting from SplitRequests from that requester. The requester shall assert DEVSEL# on allsuch Split Completions. The requester shall accept the entire byte countrequested. The requester may disconnect a Split Completion on any ADB(within the limits discussed below), but shall continue to accept thecontinuation of the Split Completion until all bytes are accepted. Ifthe requester no longer needs the Split Completion, the requester shallaccept it anyway and then discard it.

If a requester issues more than one Split Request at a time (differentSequence Numbers), the requester shall accept the Split Completions fromthe separate requests in any order. (Split Completions with the sameSequence number will always occur in ascending address order.)

In general, a requester shall have a buffer ready to receive the entirebyte count for all Split Requests it issues. A requester may disconnecta Split Completion transaction or to terminate it with Retry only underunusual circumstances that are guaranteed to resolve in a short periodof time. If a requester delays accepting Split Completion data, thatdata will be stalled in intermediate buffers in the completer and inintervening bridges. Such behavior will prevent other devices from usingthese buffers and may degrade system performance.

To prevent one requester from consuming more system buffer space than isappropriate, the length of time a requester can hold off accepting SplitCompletion transactions is limited. Preferrably, the requester shall nothold off a Split Completion transaction for more than 1 μs in any 20 μsperiod. This preferred Split Completion hold-off time is calculated asfollows for any 20 μs period:${H = {{\sum\limits_{n = 1}^{N}h_{n}} \leq {1\quad{µs}}}},{where}$

H=total hold-off time

h_(n)=n_(th) hold-off time for a Split Completion. h_(n) is measuredfrom the time the requester asserts STOP# to disconnect or terminate thetransaction with Retry, until the requester asserts TRDY# for asubsequent Split Completion transaction.

N=number of Split Completions in the 20 μs period, for all SplitRequests from a single requester.

The intent of this requirement is that the device behave well in normaluse. The actual hold-off time for a transaction is a function not onlyof when the requester is ready to accept a transaction, but also whenthe completer repeats the transaction. The Split Completion hold-offlimitation requirements are verified when the bus is idle except for asingle requester and completer and when the bus is operating at 100 MHz.It is assumed that if the device meets the maximum hold-off requirementunder these test conditions, it will behave well in normal use.

FIG. 27 illustrates how the maximum hold-off time for Split Completionsis calculated for one 20 μs period. Split Completions A and B arecompleted immediately by the requester, so hold-off time h₁ and h₂ areboth zero. Split Completions C and D terminates with Retry several timesbefore the requester is able to accept the Split Completion. Notice thecompleter issues Split Completion D before the requester accepts SplitCompletion C, indicating that the two completions are associated withdifferent Split Requests (different Sequence Numbers). The thirdhold-off time begins when the requester asserts STOP# to disconnect orterminate with Retry Split Completion C. It ends the next time therequester asserts TRDY# to resume accepting Split Completion data(“Split Completion C, completion” in the figure). Hold-off time h₄begins the next time the requester asserts STOP# for a Split Completionand ends the next time it asserts TRDY# for a Split Completion. In FIG.27 this is illustrated as the next time Split Completion D is terminatedwith Retry and when Split Completion E completes. Split Completion Dthen completes without additional hold-off the next time it is repeatedby the completer, making h₅ zero. (Split Completions D and E shall havedifferent Sequence Numbers, since the completer issued Split CompletionE before the requester accepted Split Completion D.) The total of h₁through h₅ shall be less than 1 μs.

Any completer that is ready to accept its Split Completion data at least95% of any 20 μs period automatically meets this hold-off requirement.

Bridges from one Registered PCI bus to another are exempt from thesebuffering and Retry termination limits. Since they are acting asintermediate agents for other devices that are subject to these limits,Split Completion transactions held in bridge buffers will move quicklythrough the bridge to the original requester, making room for otherSplit Completions.

Split Completion Exception Message

If an abnormal condition occurs while a completer is executing a SplitTransaction, the completer responds by sending a Split CompletionException Message to the requester. The only abnormal conditions definedherein are error conditions.

Abnormal conditions can occur in three different phases of a SplitTransaction: 1) during the Split Request, 2) during the execution of therequest by the completer, and 3) during the Split Completion.

There are no special requirements for handling an abnormal condition(that is, an error condition) that occurs during a Split Request. Allerror conditions are handled as they would be for a conventionaltransaction.

Abnormal conditions can also occur in the second phase of a SplitTransaction, after the completer has terminated a byte-count memory-readtransaction with Split Response termination. Such conditions can preventthe completer from executing the request. Examples of such conditionsinclude the following:

1. parity errors internal to the completer.

2. the byte count of the request exceeding the range of the completer.

If such a condition occurs, the completer shall notify the requester ofthe abnormal condition by sending a Split Completion Exception Messagetransaction. This transaction uses the address, command, and attributes(except the Byte Count) of the Split Completion it replaces but uses theSplit Completion Exception Message extended command. The SplitCompletion Exception Message is a byte-enable extended command, so theByte Count is unused and set to 0. The data phase for this transactionindicates the type of exception that occurred, as illustrated in Table13 hereinbelow. TABLE 13 Split Completion Exception Message AD[31:0]Split Completion Exception Message 0000 0000h Other Completer Error. Thecompleter uses this message if it encountered an error that preventsexecution of the Split Request, and the error is not indicated by one ofthe other exception messages. For example, a PCI-to-PCI bridge thatencountered a Target-Abort on the destination bus would respond withthis message. Note that such an error could occur at the beginning ofthe Sequence or at any continuation of the Sequence after adisconnection. 0000 0001h Byte Count Out of Range. The completer usesthis message if the sum of the address and the byte count of the SplitRequest exceeds the address range of the completer. The Completer ispermitted either to send this message in lieu of a Split Completion, orto send Split Completion data up to the device boundary, disconnect onthe device boundary, and then send this message in lieu of continuingthe Sequence. all other Reserved. values

If the error occurs at the beginning of the transaction, the completersends a Split Completion Exception Message in lieu of the initial SplitCompletion. After a normal disconnection of the Split Completion thecompleter may send a Split Completion Exception Message in lieu of thecontinuation of the Split Completion. Once the exception message hasbeen sent, the rest of the Split Completion is discarded, regardless ofhow many bytes remain to be sent.

A variety of abnormal conditions can occur during the third phase of theSplit Transaction, which is the Split Completion transaction. If theSplit Completion transaction completes with either Master-Abort orTarget-Abort, the requester is indicating a failure condition thatprevents it from accepting the data it requested. In this case if theSplit Request addresses a prefetchable location, the completer shalldiscard the Split Completion and take no further action. If the locationis not prefetchable, the completer shall discard the Split Completion,set the Split Completion Discarded bit in the Registered PCI StatusRegister, and assert SERR# (if enabled).

A Split Completion normally will terminate with data transfer or withRetry. The requester is limited as to the length of time it canterminate with Retry before it shall accept the data. The requester ispermitted to disconnect the Split Completion but is obligated eventuallyto take all the data. A properly functioning requester will eventuallyuse some termination other than Retry and will take all the dataindicated by the Byte Count of the original Split Request.

For completeness the completer's response to the abnormal terminations,Master-Abort and Target-Abort, is specified. The transaction wouldterminate with Master-Abort if the requester did not recognize theSequence ID of the Split Completion. This condition could occur becausethe requester was reset and is no longer expecting the Split Completion.Such conditions do not occur frequently but sometimes occur when adevice driver is manually unloaded, or the device encounters an errorthat required the driver to reset the device. The Split Completion wouldterminate with Target-Abort if the address or Byte Count becamecorrupted, or if the requester encountered an internal error thatprevented it from taking the Split Completion.

If the requester detects a data parity error during a Split Completion,it asserts PERR# if enabled and sets bit 15 (Detected Parity Error) inthe Status register. The requester also sets bit 8 (Master Data ParityError) in the Status register, because it was the original initiator ofthe Sequence (even though the completer is the initiator of the SplitCompletion).

Unexpected Split Completion Exceptions

The requester shall accept all Split Completions transactions with therequester's Bus Number and Initiator Number. If the claimed SplitCompletion is identified as an unexpected Split Completion by therequester, the requester still shall accept the Split Completiontransaction in its entirety and discard the data. In addition todiscarding the data the device shall set the Unexpected Split Completionstatus bit in the Registered PCI Status Register and notify its devicedriver of the exception. If notification of the device driver is notpossible the requestor shall assert SERR#, if enabled.

When identifying Split Completions transactions, the requester shallvalidate the Split Completion transaction Sequence Number againstoutstanding Split transactions. In addition to qualifying SplitCompletion transaction with Sequence Number, the requester canadditionally compare address and/or Byte-Count against outstanding SplitRequest.

Transaction Termination

Referring now to FIGS. 28-42, methods by which transactions can beterminated are illustrated in schematic timing diagrams, according tothe Registered PCI invention. The following termination methods will bedescribed hereinbelow: 1) Disconnect with Data, 2) Target Retry, 3)Split Response Termination, 4) Master-Abort, and 5) Target-Abort. Forsimplification in the disclosure of the Registered PCI invention, theFIGS. 28-42 which illustrate transaction termination show DEVSEL# timingA, and no target initial wait states. However it is within the scope ofthe invention and contemplated herein that all other legal DEVSEL#timings and wait state combinations are also possible.

Disconnect With Data

Initiator Termination and Disconnection

Referring now to FIGS. 28-31: FIG. 28 illustrates a schematic timingdiagram of a Byte-Count Transaction with 4 or more Data Phases,Initiator Disconnection at ADB or Termination at Byte Count. FIG. 29illustrates a schematic timing diagram of a Byte-Count TransactionStarting 3 Data Phases from ADB, Initiator Disconnection at ADB orTermination at Byte Count. FIG. 30 illustrates a schematic timingdiagram of a Byte-Count Transaction Starting 2 Data Phases from ADB,Initiator Disconnection at ADB or Termination at Byte Count. FIG. 31illustrates a schematic timing diagram of a Byte-Count TransactionStarting 1 Data Phase from ADB, Initiator Disconnection at ADB orTermination at Byte Count.

Transactions that are disconnected by the initiator on an ADB before thebyte count has been satisfied and those that terminate at the end of thebyte count appear the same on the bus. The following figures illustrateinitiator disconnection or termination for transactions with 4 or moredata phases and for transactions with less than four data phases. InFIG. 28, the initiator disconnects or terminates after 4 or more dataphases. In this case the initiator signals the end of the transaction bydeasserting FRAME# 1 clock before the last data phase. In FIGS. 29-31,the initiator disconnects or terminates after 3, 2, and 1 data phases,respectively. In this case the initiator signals disconnection bysetting the Disconnect on First ADB attribute bit. (Termination occursat the end of the byte count). In FIG. 29, the initiator deassertsFRAME# for a 3 data phase transaction, 1 clock after the Initiatordetects the assertion of the sampled TRDY#. In FIGS. 30 and 31, theinitiator deasserts FRAME# for a 2 and a 1 data phase transaction,respectively, showing the FRAME# deassertion occurring with IRDY#.

Target Disconnection

Referring now to FIGS. 32-35, timing diagrams for target disconnectionon an ADB for transactions with 4 or more data phases and fortransactions with less than four data phases are illustrated.:

FIG. 32 illustrates a schematic timing diagram of a Byte-CountTransaction with 4 or More Data Phases, Target Disconnect with Data atADB. Shown in FIG. 32 is a target disconnection on an ADB after 4 ormore data phases, with the target signaling disconnection by assertingSTOP# 3 clock before the last data phase.

FIG. 33 illustrates a schematic timing diagram of a Byte-CountTransaction Starting 3 Data Phases from ADB, Target Disconnect with Dataat ADB, Decode “A,” 0 Initial Wait States. FIG. 34 illustrates aschematic timing diagram of a Byte-Count Transaction Starting 2 DataPhases from ADB, Target Disconnect with Data at ADB, Decode “A,” 0Initial Wait States. FIG. 35 illustrates a schematic timing diagram of aByte-Count Transaction Starting 1 Data Phases from ADB, TargetDisconnect with Data at ADB, Decode “A,” 0 Initial Wait States. FIGS.33-35 illustrate target disconnection on an ADB after 3, 2, and 1 dataphases, respectively, with the target signaling disconnection byasserting STOP# with TRDY#.

Target Retry Termination

Byte-Count Transactions

Referring to FIG. 36, a schematic timing diagram of a Byte-CountTransaction Showing Target Retry termination of a byte-count transactionis illustrated.

Byte-Enable Transactions

Referring to FIG. 37, a schematic timing diagram of a Byte-EnableTransaction Showing Target Retry termination of a byte-enabletransaction is illustrated.

Split Response Termination

Referring to FIG. 38, a schematic timing diagram of a Split ResponseTermination of a Byte-Count Memory-Read Transaction is illustrated.

Master-Abort Termination

Byte-Count Transactions

Referring to FIG. 39, a schematic timing diagram of a Master-AbortTermination of a Byte-Count Transaction is illustrated.

Byte-Enable Transactions

Referring to FIG. 40, a schematic timing diagram of a Master-AbortTermination of a Byte-Enable Transaction is illustrated.

Target-Abort Termination

Referring to FIGS. 41 and 42, schematic timing diagrams for target abortfor Byte-Count and Byte-Enable transactions, respectively areillustrated. In FIGS. 41 and 42, the initiator keeps FRAME# and IRDY#asserted 1 clock passed the target signaling termination with thedeassertion of DEVSEL# and STOP#, this is called overshoot. Overshootoccurs as a result of the bus protocol requiring devices to sample thebus signal only after the input signal has been flopped through aregister. This results in the initiator or target experiencing a 1 clocklag in responding to any signal changes on the bus, see Byte-CountTransactions hereinabove which shows the Initiator and target views ofthe bus.

Byte-Count Transactions

FIG. 41 illustrates a schematic timing diagram of a Target-AbortTermination of a byte-count transaction.

Byte-Enable Transactions

FIG. 42 illustrates a schematic timing diagram of a Target-Aborttermination of a byte-enable transaction.

Bus Width

According to a preferred embodiment of the invention, Registered PCIdevices have a 64-bit AD bus. However, it is contemplated and within thescope of the claimed invention that Registered PCI devices may alsooperate as 32-bit devices. The 32-bit embodiment of the Registered PCIdevices are described hereinafter. The 64-bit Registered PCI deviceembodiments would need to follow the requirements desribed hereinbelow,i.e., if a 32-bit device addressed a 64-bit device.

In this 32-bit embodiment the requirements that apply only to 32-bitdevices or to 64-bit devices that are designed to operate with those32-bit devices are marked with an asterisk (*). These requirements areoptional for devices designed exclusively for 64-bit operation.Requirements not marked with an asterisk are required of all RegisteredPCI devices.

Data Transfer Width

Registered PCI support for varying the width of data transfers minimizesthe changes from the corresponding support in conventional PCI. Thefollowing requirements for Registered PCI are the same as forconventional PCI:

1. Only memory transactions use 64-bit data transfers. All othertransactions use 32-bit data transfers.

2. 64-bit addressing is independent of the width of the data transfers.

3. A 64-bit initiator asserts REQ64# with the same timing as FRAME# torequest a 64-bit data transfer. It deasserts REQ64# with FRAME# at theend of the transaction.

4. If a 64-bit target is addressed by a transaction that does not haveREQ64# asserted with FRAME#, the target shall not assert ACK64# andshall complete the transaction as a 32-bit target.

5. If a 64-bit target is addressed by a transaction that does haveREQ64# asserted with FRAME#, the target asserts ACK64# with DEVSEL# tocomplete the transaction as a 64-bit target. It deasserts ACK64# withDEVSEL# at the end of the transaction.

6. If the target does not assert ACK64#, the transaction will proceed asa 32-bit transaction. During data phases the initiator is permitted todrive any value on C/BE[7:4] and (for a write transaction) AD[63:32].

The following requirements for Registered PCI are different fromconventional PCI:

1. Only byte-count memory transactions use 64-bit transfers. Byte-enablememory transactions use 32-bit transfers.

2. Wait-state requirements and Allowable Disconnect Boundaries areunaffected by the width of the data transfer.

3. The attribute phase is always a single clock, regardless of the sizeof the initiator or the target. Registered PCI devices shall implement abit in the Registered PCI Command register called Use 32-bit Attribute.If this bit is set, the initiator will set the upper 32 bits of theattribute to 0 on all transactions. System configuration software willset this bit to prevent aliasing problems when 64-bit attributes areviewed by 32-bit devices.

4. AD[2] shall match the starting byte address of the transaction whenthe initiator requests a 64-bit data transfer. (Conventional PCIrequires AD[2] to be zero because the byte enables indicate the actualstarting address.)

5. The extended command is always driven on C/BE[3:0]. C/BE[7:4] arereserved during the attribute phase and driven to a high logic voltageby 64-bit initiators.

6. * If a 64-bit initiator is starting a write transaction and AD[2] ofthe starting byte address is 1 (that is, the first byte of thetransaction is in the upper 32-bits of the bus), the 64-bit initiatorshall duplicate the write data from the upper 32 bits of the bus ontothe lower 32 bits of the bus.

FIG. 43 illustrates a schematic timing diagram of a 64-bit Read Requestwith 32-bit Transfer Starting on Even DWORD. FIG. 44 illustrates aschematic timing diagram of a 64-bit Read Request with 32-bit TransferStarting on Odd DWORD. FIG. 45 illustrates a schematic timing diagram ofa 64-bit Write Request with 32-bit Transfer Starting on Even DWORD. FIG.46 illustrates a schematic timing diagram of a 64-bit Write Request with32-bit Transfer Starting on Odd DWORD. The timing diagram of FIG. 46illustrates the data steering that is required by a 64-bit initiatorwhen supporting 32-bit devices. This data steering need only occur whenthe 64-bit initiator is negotiating a 64-bit data transaction with a oddDWORD starting address. To satisfy the steering requirement, theinitiator shall duplicate the high DWORD data onto the lower AD buslanes [31:0] in preparation for a 32-bit target claiming thetransaction. The initiator confirms a 32-bit target has claimed thetransaction in the Target Response Phase of the transaction, whenDEVSEL# assertion is detected without ACK64# assertion. Note that FIG.46 illustrates an initiator termination on an even DWORD, which can onlyoccur if the byte count is satisfied in that DWORD. (An ADB occurs afteran odd DWORD.)

Address Width

The Registered PCI invention supports varying the address width. Thisminimizes the changes required for Registered PCI from the correspondingsupport in conventional PCI. Additional requirements for Registered PCIpermit timing optimization for the case in which all devices on the bushave a 64-bit data path.

The following requirements for Registered PCI are the same as forconventional PCI:

1. If the address of a transaction is less than 4 GB, the following areall true:

-   -   a. The transaction uses a single address cycle.    -   b. During the address phase AD[63:32] are zero, and AD[3 1:0]        contain the address.    -   c. During the address phase C/BE[3:0]# contain the transaction        command, and C/BE[7:4]# are reserved.

2. * If the address of a transaction is greater than 4 GB, the initiatoruses a dual address cycle in two cases. The first is if the initiatorhas a 32-bit bus. The second is if the initiator has a 64-bit bus andits Use Dual Address Cycle bit in the Registered PCI Command register isset. In the first case (32-bit device) the following are all true:

-   -   a. The transaction uses a dual address cycle.    -   b. In the first address phase AD[3 1:0] contain the lower half        of the address. In the second address phase AD[31:0] contain the        upper half of the address.    -   c. In the first address phase C/BE#[3:0] contain the Dual        Address Cycle command. In the second address phase C/BE#[3:0]        contain the actual transaction command

In the second case (64-bit device with Use Dual Address Cycle bit set)the following are all true:

-   -   a. The transaction uses a dual address cycle.    -   b. In the first address phase AD[63:32] contain the upper half        of the address, and AD[31:0] contain the lower half of the        address. In the second address phase AD[63:32] and AD[31:0]        contain duplicate copies of the upper half of the address.    -   c. In the first address phase C/BE[3:0]# contain the Dual        Address Cycle command and C/BE[7:4]# contain the transaction        command. In the second address phase C/BE[3:0]# and C/BE[7:4]#        contain duplicate copies of the transaction command.

3. * DEVSEL# timing designations are delayed one clock for transactionswith a dual address cycle. For example, decode speed A after a dualaddress cycle is the same as decode speed B after a single addresscycle, just as in conventional PCI Fast decode speed after a dualaddress cycle is the same as Medium decode speed after a single addresscycle. Note that it is theoretically possible for a 64-bit target todecode its address after only the first address phase of a dual addresscycle and be ready to assert DEVSEL# sooner than decode speed A. Howeverno device is permitted to assert DEVSEL# sooner than the first clockafter the attribute phase.

4. The rest of the transaction proceeds identically after either asingle address cycle or a dual address cycle.

The following requirements for Registered PCI are different fromconventional PCI:

1. All addresses are preferrably 64-bits long.

2. * 32-bit Registered PCI devices shall support 64-bit addressing. All32-bit initiators shall generate a dual address cycle for addressesgreater than 4 GB. All 32-bit targets that include memory Base AddressRegisters shall implement the 64-bit versions. All memory rangeregisters in 32-bit PCI-to-PCI bridges shall support the 64-bit versionsof those registers. It is contemplated and within the scope of theinvention that system configuration software may assign allnon-prefetchable memory ranges below 4 GB. Non-prefetchable memoryranges are typically used for control operations, which are oftenaccessed from time-critical software routines. Such accesses will befaster if the address is below 4 GB, so a single address cycle is used.

3. All Registered PCI devices support a status bit indicating the sizeof their bus.

4. * 64-bit Registered PCI devices include an bit in the Registered PCICommand register, called Use Dual Address Cycle, that controlsgeneration of dual address cycles. If this bit is set, the device uses adual address cycle when initiating any transaction with an addressgreater than 4 GB. If the bit is reset, the device uses a single addresscycle for all addresses. System configuration software sets this bit inall devices that reside on a bus containing at least one 32-bit device.

FIG. 47 illustrates a 64-bit initiator executing a Dual Address Cyclefor a 64-bit Byte-Count Memory-Read transaction. The initiator drivesthe entire address (lower address on AD[31:00] and upper address onAD[63:32]) and both commands (DAC “1101” on C/BE[3:0]# and the actualbus command on C/BE[7:4]#) all during the initial address phase at clock3. On the second address phase, the initiator drives the upper addresson AD[31:0] (and AD[63:32]) while the bus command is driven onC/BE[3:0]# (and C/BE[7:4]#). The initiator immediately follows thesecond address phase with the one clock attribute phase in clock 5, allthe upper attribute bits AD[63:32] are set to 0, to prevent Sequence IDaliasing when supporting 32-bit devices. Unlike conventional PCI 64-bittargets, Registered PCI 64-bit targets when supporting DAC, adjust theirDEVSEL# assertion by one clock since DEVSEL# is not asserted any earlierthan the clock after the attributed phase, as shown in clock 6 fordevice timing A.

Transaction Ordering and Deadlock-Avoidance

According to the Registered PCI invention, two features are introducedthat affect transaction ordering and deadlock-avoidance that are notpresent in conventional PCI. The rest of the ordering anddeadlock-avoidance rules are the same as conventional PCI.

Ordering and Passing Rules

According to the Registered PCI invention, the first new feature thataffects ordering rules is the Relaxed Ordering attribute bit. If thisattribute bit is set for a memory-write transaction, that transaction ispermitted to pass previously posted memory-write transactions. If thisattribute is set for a read transaction, the completion for thattransaction is permitted to pass previously posted memory-writetransactions. Refer to Relaxed Ordering Rules hereinbelow for adiscription of the application of this bit.

The second new feature is Split Transaction. Split Transaction orderingand deadlock-avoidance rules are almost identical to the rules forDelayed Transactions. In all cases the requirements for Split ReadRequest are identical to those for Delayed Read Requests. The order ofmemory read transactions is established when the transaction completes.Split Read Requests can be reordered with other Split Read Requests andwith Delayed Requests. If an initiator is concerned about the order inwhich two Split Read Requests are completed, the initiator shall notissue the second request until the first one completes.

A Split Read Completion has the same ordering requirements as a DelayedRead Completion, except that Split Read Completions with the sameSequence ID (that is, Split Read Completion transactions that originatefrom the same Split Read Request) shall stay in address order. Thecompleter shall supply the Split Read Completions on the bus in addressorder, and any intervening bridges shall preserve this order. Thisguarantees that the requester will always receive the data in itsnatural order. Split Read Completions with different Sequence IDs haveno ordering restrictions. In this sense such Split Read Completions arelike Delayed Read Completions.

Table 14 hereinbelow lists the ordering requirements for all SplitTransactions, Delayed Transactions and posted memory-write transactions.The columns represent the first of two transactions, and the rowsrepresent the second. The table entry indicates what a device operatingon both transactions is required to do. The preferred choices are:

Yes—the second transaction shall be allowed to pass the first to avoiddeadlock.

Y/N—there are no requirements. The device may optionally allow thesecond transaction to pass the first or be blocked by it.

No—the second transaction shall not be allowed to pass the firsttransaction. This is required to preserve strong write ordering.

The following is a list of definitions for abbreviated terms used whendescribing transaction ordering. Abbreviation Definition PMW PostedMemory Write DRR Delayed Read Request SRR Split Read Request DWR DelayedWrite Request DRC Delayed Read Completion SRC Split Read Completion DWCDelayed Write Completion DR Delayed Read DC Delayed Completion RR ReadRequest RC Read Completion

TABLE 14 Transactions Ordering and Deadlock-Avoidance Rules PMW DRR &SRR DWR DRC & SRC DWC Row pass (Col 2) (Col 3) (Col 4) (Col 5) (Col 6)PMW a) No Yes Yes Yes Yes (Row A) b) Y/N DRR & SRR No Y/N Y/N Y/N Y/N(Row B) DWR No Y/N Y/N Y/N Y/N (Row C) DRC & SRC a) No Yes Yes a) Y/NY/N (Row D) b) Y/N b) No DWC Y/N Yes Yes Y/N Y/N (Row E)

-   A2 a In general, PMW shall stay in order. (Same a conventional PCI.)-   A2 b If Relaxed Ordering attribute is set, then that PMW is    permitted to pass other PMW.

Also, subsequent PMW (i.e. PMW in which the Initial Sequence bit iscleared) is permitted to pass other PMW with different Sequence ID.

-   A3-A6 PMW shall be allowed to pass DRs and DCs to avoid deadlocks.    (Same as conventional PCI.) SRR and SRC have the same requirements    as DRR and DRC.-   B2 Read Requests cannot can pass a PMW (strong write ordering).    (Same as conventional PCI.)-   B3-B6 DRR can be blocked or pass other DRs and DCs. (Same as    conventional PCI.) SRR and SRC have the same requirements as DRR and    DRC.-   C2 DWR cannot pass a PMW (strong write ordering). (Same as    conventional PCI.) Although in theory, the Relaxed Ordering    attribute could be used to enable DWR to pass a PMW, there would be    little application for such a feature, so it is not allowed.-   C3-C6 DWR can be blocked or pass other DRs and DCs. (Same as    conventional PCI.) SRR and SRC have the same requirements as DRR and    DRC.-   D2 a In general, Read Completions cannot pass a PMW (strong write    ordering). (Same as conventional PCI.)-   D2 b If Relaxed Ordering attribute bit is set, then that DRC or SRC    is permitted to pass PMW.-   D3-D4 DRC shall be allowed to pass DRs to avoid deadlocks. (Same as    conventional PCI.) SRC has the same requirements as DRC.-   D5 a DRC can be blocked or pass other DCs. (Same as conventional    PCI.) SRCs with different Sequence ID have the same requirements as    DRC.-   D5 b SRCs with the same Sequence ID shall remain in address order.    No deadlock here because they will all eventually complete.-   D6 DRC can be blocked or pass other DCs. (Same as conventional PCI.)    SRC has the same requirements as DRC.-   E2 Writes moving in opposite direction have no ordering    relationship. (Same as conventional PCI.)-   E3-E4 DWC shall be allowed to pass DRs to avoid deadlocks. (Same as    conventional PCI.) SRR has the same requirements as DRR.-   E5-E6 DWC can be stalled or pass other DCs. (Same as conventional    PCI.) SRC has the same requirements as DRC.

Required Acceptance Rules

The Registered PCI invention has the same requirement for acceptingtransactions as conventional PCI, with one exception describedhereinbelow. Using the terminology of the PCI Specification incorporatedby reference herein, a “simple device” (i.e. one that does not dooutbound write posting) can never (with the exception describedhereinbelow) make the acceptance of a transaction as a target contingentupon the prior completion of another transaction as an initiator. A“bridge device” (i.e. one that does outbound write posting) can nevermake the acceptance (posting) of a memory-write transaction as a targetcontingent on the prior completion of a transaction as an initiator onthe same bus. Furthermore, to provide backward compatibility withPCI-to-PCI bridges designed to revision 1.0 of the PCI-to-PCI BridgeArchitecture Specification, incorporated by reference herein, alldevices are required to accept memory-write transactions even whileexecuting a previously enqueued Delayed Transaction. A device ispermitted to terminate a memory-write transaction with Retry only fortemporary conditions that are guaranteed to resolve over time (aslimited by the Max Completion ECR). Bridge devices are permitted torefuse to accept non-posted transactions as a target until the devicecompletes its memory-write transactions as an initiator.

Split Completions are the exceptions to these conventional rules forRegistered PCI devices. Any Registered PCI device that is completing aSplit Transaction (a completer) is also permitted to refuse to accept anon-posted transaction as a target until it finishes its SplitCompletion as an initiator.

The requester can not make the acceptance of a Split Completion as atarget contingent on the prior completion of a transaction of any kind(posted or non-posted) as an initiator on the same bus. The requester ispermitted to terminate a Split Completion with Retry for temporaryconditions that are guaranteed to resolve with time (as limited byRequirements for Accepting Split Completions hereinabove). Otherwise, adeadlock may occur.

Transaction Sequence Combining and Re-ordering

A Buffer managers is allowed to re-order subsequent byte-countmemory-write transaction (transactions with the Initial Sequence Requestbit not set). If the Initial Sequence Request bit is not set for abyte-count memory write transaction, the buffer manager is then allowedto re-order the transaction allowing it to pass all transactions that donot match the byte-count memory-write transaction's Sequence ID. Thisallows buffer manager to combine and re-order subsequent byte-countmemory-write transaction with byte-count memory-write transactionshaving the same Sequence ID, while maintaining address order relative tothe Sequence ID. The following rules shall be applied when supportingtransaction sequence combining and re-ordering:

1. Buffer manangers on detecting a byte-count memory-write transactionswith the Initial Sequence Request attribute bit set and the RelaxOrdered attribute not set shall follow the same ordering rules as inconventional PCI.

2. Buffer managers on detecting a subsequent byte-count memory-writetransaction (Initial Sequence Request bit not set) and the Relax Orderedattribute not set are allowed to combine the subsequence byte-countmemory-write transaction with buffered transactions having the sameSequence ID, while maintaining address order relative to the SequenceID.

3. Transaction sequence combining is allowed regardless of the number oftransactions that has occurred after the transaction sequence wasdisconnected and before the initiator is able to continue thetransaction sequence with a subsequent transaction.

4. Buffer managers on detecting a subsequent byte-count memory-writetransaction (Initial Sequence Request bit not set) and the Relax Orderedattribute not set are allowed to re-order the subsequent byte-countmemory-write transaction relative to any other transaction as long asthe Sequence ID does not match.

It is contemplated and with the scope of the Registered PCI inventionthat All Split Completions follow identical ordering and combining rulesfor subsequent byte-count memory-write transactions. That is, SplitCompletions are allowed to pass other transactions that have a differentSequence ID and are therefore only required to maintain orderingrelative to its Sequence ID. Any memory-writes transaction with theRelax Ordered attribute set is allowed to pass any other transactions,including other transactions with the same Sequence ID.

The present invention, therefore, is well adapted to carry out theobjects and attain the ends and advantages mentioned, as well as othersinherent therein. While the present invention has been depicted,described, and is defined by reference to particular preferredembodiments of the invention, such references do not imply a limitationon the invention, and no such limitation is to be inferred. Theinvention is capable of considerable modification, alternation, andequivalents in form and function, as will occur to those ordinarilyskilled in the pertinent arts. The depicted and described preferredembodiments of the invention are exemplary only, and are not exhaustiveof the scope of the invention. Consequently, the invention is intendedto be limited only by the spirit and scope of the appended claims,giving full cognizance to equivalents in all respects.

1. A device that is adapted to send information in accordance with acommunication protocol, comprising: a structure that is adapted to issuea command representative of a default handling of a transaction; and astructure that is adapted to issue an attribute associated with thecommand to provide information that modifies the default handling of thetransaction.
 2. The device set forth in claim 1 wherein the attributeand a sequence identifier are issued during an attribute phase.
 3. Thedevice set forth in claim 1 wherein the attribute and a byte count areissued in an attribute phase.
 4. The device set forth in claim 1,wherein the communication protocol defines communication betweenperipheral devices in a computer system.
 5. The device set forth inclaim 1, wherein the communication protocol comprises a peripheralcomponent interconnect protocol.
 6. The device set forth in claim 1,wherein the default handling comprises a snoop operation and theattribute comprises an indication that the snoop operation is not to beperformed.
 7. The device set forth in claim 4, wherein the snoopoperation is performed in support of a hardware-enforced cache coherencyrequirement.
 8. The device set forth in claim 1, wherein the defaulthandling of the transaction requires the snoop operation to be performedin support of a hardware-enforced cache coherency requirement.
 9. Thedevice set forth in claim 1, wherein the device comprises an integratedcircuit.
 10. The device set forth in claim 9, wherein the integratedcircuit comprises an application-specific integrated circuit.
 11. Thedevice set forth in claim 1, wherein the default handling comprises astrongly ordered scheme and the attribute comprises an indication thatthe strongly ordered condition is to be replaced by a relaxed orderingscheme.
 12. A device that is adapted to send information according to acommunication protocol, comprising: a structure that is adapted to issuea command representative of a default handling of a transaction; and astructure that is adapted to selectively issue an attribute thataugments the default handling of the transaction.
 13. The device setforth in claim 12 wherein the attribute and a sequence identifier areissued during an attribute phase.
 14. The device set forth in claim 12wherein the attribute and a byte count are issued in an attribute phase.15. The device set forth in claim 12, wherein the communication protocoldefines communication between peripheral devices in a computer system.16. The device set forth in claim 12, wherein the communication protocolcomprises a peripheral component interconnect protocol.
 17. The deviceset forth in claim 12, wherein the default handling comprises a snoopoperation and the attribute comprises an indication that the snoopoperation is not to be performed.
 18. The device set forth in claim 17,wherein the default handling of the transaction requires the snoopoperation to be performed in support of a hardware-enforced cachecoherency requirement.
 19. The device set forth in claim 12, wherein thedefault handling comprises a strongly ordered scheme and the attributecomprises an indication that the strongly ordered condition is to bereplaced by a relaxed ordering scheme.
 20. The device set forth in claim12, wherein the device comprises an integrated circuit.
 21. The deviceset forth in claim 21, wherein the integrated circuit comprises anapplication-specific integrated circuit.
 22. A method of operating adevice in compliance with a defined communication strategy, the methodcomprising: issuing a command that represents a default handling of atransaction; and issuing an attribute that provides information tomodify the default handling of the transaction.
 23. The method set forthin claim 22 wherein the attribute and a sequence identifier are issuedduring an attribute phase.
 24. The device set forth in claim 22 whereinthe attribute and a byte count are issued in an attribute phase.
 25. Themethod set forth in claim 22, wherein the defined communication strategydefines communication between peripheral devices in a computer system.26. The method set forth in claim 22, wherein the defined communicationstrategy comprises a peripheral component interconnect protocol.
 27. Themethod set forth in claim 22, comprising: performing a snoop operationif the default handling of the transaction is not modified by theattribute, and; refraining from performing the snoop operation if theattribute indicates that the default handling of the transaction is tobe modified.
 28. The method set forth in claim 27, wherein the defaulthandling of the transaction requires the snoop operation to be performedin support of a hardware-enforced cache coherency requirement.
 29. Themethod set forth in claim 22, comprising: performing the transactionaccording to a strongly ordered scheme if the default handling of thetransaction is not modified by the attribute, and performing thetransaction according to a relaxed ordering scheme if the attributeindicates that the default handling of the transaction is to bemodified.
 30. A tangible medium, comprising: machine-readableinstructions adapted to issue a command in accordance with acommunication protocol, the command being representative of a defaulthandling of a transaction; and machine-readable instructions adapted toissue an attribute that provides information to allow modification ofthe default handling of the transaction.
 31. A device that is adapted tosend information in accordance with a communication protocol,comprising: means for issuing a command that represents a defaulthandling of a transaction; and means for issuing an attribute thatprovides information to modify the default handling of the transaction.